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NAME

       erl_syntax - Abstract Erlang syntax trees.

DESCRIPTION

       Abstract Erlang syntax trees.

       This  module  defines  an abstract data type for representing Erlang source code as syntax
       trees, in a way that is backwards compatible with  the  data  structures  created  by  the
       Erlang standard library parser module erl_parse (often referred to as "parse trees", which
       is a bit of a misnomer). This means that all erl_parse trees  are  valid  abstract  syntax
       trees,  but  the  reverse is not true: abstract syntax trees can in general not be used as
       input to functions expecting an erl_parse tree. However, as long  as  an  abstract  syntax
       tree  represents  a  correct  Erlang  program,  the  function  revert/1  should be able to
       transform it to the corresponding erl_parse representation.

       A recommended starting  point  for  the  first-time  user  is  the  documentation  of  the
       syntaxTree() data type, and the function type/1.

       NOTES:

       This module deals with the composition and decomposition of syntactic entities (as opposed
       to semantic ones); its purpose is to hide all direct references  to  the  data  structures
       used  to  represent  these  entities.  With  few  exceptions, the functions in this module
       perform no semantic interpretation of their inputs, and in general, the user is assumed to
       pass type-correct arguments - if this is not done, the effects are not defined.

       With  the  exception  of  the  erl_parse  data structures, the internal representations of
       abstract syntax trees are subject to change without notice, and should not  be  documented
       outside  this module. Furthermore, we do not give any guarantees on how an abstract syntax
       tree may or may not be represented, with the  following  exceptions:  no  syntax  tree  is
       represented by a single atom, such as none, by a list constructor [X | Y], or by the empty
       list []. This can be relied on when writing functions that operate on syntax trees.

DATA TYPES

         erl_parse() = parse_tree() (see module erl_parse):

           The "parse tree" representation built by the Erlang standard library parser erl_parse.
           This is a subset of the syntaxTree type.

         forms() = syntaxTree() | [syntaxTree()]:

         syntaxTree():

           An  abstract syntax tree. The erl_parse "parse tree" representation is a subset of the
           syntaxTree() representation.

           Every abstract syntax tree node has a type, given by the function  type/1.  Each  node
           also has associated attributes; see get_attrs/1 for details. The functions make_tree/2
           and subtrees/1 are generic constructor/decomposition  functions  for  abstract  syntax
           trees.  The  functions abstract/1 and concrete/1 convert between constant Erlang terms
           and their syntactic representations. The  set  of  syntax  tree  nodes  is  extensible
           through the tree/2 function.

           A  syntax  tree  can  be transformed to the erl_parse representation with the revert/1
           function.

         syntaxTreeAttributes():

           This is an abstract representation of syntax tree node attributes;  see  the  function
           get_attrs/1.

EXPORTS

       abstract(Term::term()) -> syntaxTree()

              Returns  the  syntax  tree  corresponding to an Erlang term. Term must be a literal
              term, i.e., one that can be represented as a source code literal. Thus, it may  not
              contain  a  process  identifier,  port,  reference,  binary  or function value as a
              subterm. The function recognises printable strings, in order to get a  compact  and
              readable  representation.  Evaluation  fails  with  reason  badarg if Term is not a
              literal term.

              See also: concrete/1, is_literal/1.

       add_ann(Annotation::term(), Node::syntaxTree()) -> syntaxTree()

              Appends the term Annotation to the list of user annotations of Node.

              Note: this is  equivalent  to  set_ann(Node,  [Annotation  |  get_ann(Node)]),  but
              potentially more efficient.

              See also: get_ann/1, set_ann/2.

       add_postcomments(Comments::[syntaxTree()], Node::syntaxTree()) -> syntaxTree()

              Appends Comments to the post-comments of Node.

              Note:  This  is  equivalent  to  set_postcomments(Node,  get_postcomments(Node)  ++
              Comments), but potentially more efficient.

              See  also:  add_precomments/2,  comment/2,   get_postcomments/1,   join_comments/2,
              set_postcomments/2.

       add_precomments(Comments::[syntaxTree()], Node::syntaxTree()) -> syntaxTree()

              Appends Comments to the pre-comments of Node.

              Note:   This   is  equivalent  to  set_precomments(Node,  get_precomments(Node)  ++
              Comments), but potentially more efficient.

              See  also:  add_postcomments/2,  comment/2,   get_precomments/1,   join_comments/2,
              set_precomments/2.

       application(Operator::syntaxTree(), Arguments::[syntaxTree()]) -> syntaxTree()

              Creates an abstract function application expression. If Arguments is [A1, ..., An],
              the result represents "Operator(A1, ..., An)".

              See also: application/3, application_arguments/1, application_operator/1.

       application(Module, Function::syntaxTree(), Arguments::[syntaxTree()]) -> syntaxTree()

              Types:

                 Module = none | syntaxTree()

              Creates an abstract function application expression. If Module  is  none,  this  is
              call  is equivalent to application(Function, Arguments), otherwise it is equivalent
              to application(module_qualifier(Module, Function), Arguments).

              (This is a utility function.)

              See also: application/2, module_qualifier/2.

       application_arguments(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of argument subtrees of an application node.

              See also: application/2.

       application_operator(Node::syntaxTree()) -> syntaxTree()

              Returns the operator subtree of an application node.

              Note: if Node represents "M:F(...)", then the result is  the  subtree  representing
              "M:F".

              See also: application/2, module_qualifier/2.

       arity_qualifier(Body::syntaxTree(), Arity::syntaxTree()) -> syntaxTree()

              Creates an abstract arity qualifier. The result represents "Body/Arity".

              See also: arity_qualifier_argument/1, arity_qualifier_body/1.

       arity_qualifier_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument (the arity) subtree of an arity_qualifier node.

              See also: arity_qualifier/2.

       arity_qualifier_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of an arity_qualifier node.

              See also: arity_qualifier/2.

       atom(Name) -> syntaxTree()

              Types:

                 Name = atom() | string()

              Creates  an  abstract  atom  literal.  The  print name of the atom is the character
              sequence represented by Name.

              See also: atom_literal/1, atom_name/1, atom_value/1, is_atom/2.

       atom_literal(Node::syntaxTree()) -> string()

              Returns the literal string represented by an atom node. This  includes  surrounding
              single-quote characters if necessary.

              Note  that  e.g.  the  result  of  atom("x\ny")  represents  any and all of 'x\ny',
              'x\12y', 'x\012y' and 'x\^Jy\'; cf. string/1.

              See also: atom/1, string/1.

       atom_name(Node::syntaxTree()) -> string()

              Returns the printname of an atom node.

              See also: atom/1.

       atom_value(Node::syntaxTree()) -> atom()

              Returns the value represented by an atom node.

              See also: atom/1.

       attribute(Name) -> syntaxTree()

              Equivalent to attribute(Name, none).

       attribute(Name::syntaxTree(), Args::Arguments) -> syntaxTree()

              Types:

                 Arguments = none | [syntaxTree()]

              Creates an abstract program attribute. If Arguments is [A1, ...,  An],  the  result
              represents  "-Name(A1,  ...,  An).".  Otherwise,  if  Arguments is none, the result
              represents "-Name.". The latter form makes it possible  to  represent  preprocessor
              directives such as "-endif.". Attributes are source code forms.

              Note:  The  preprocessor  macro  definition  directive  "-define(Name,  Body)." has
              relatively few requirements on the syntactical form of Body (viewed as  a  sequence
              of  tokens).  The text node type can be used for a Body that is not a normal Erlang
              construct.

              See also: attribute/1, attribute_arguments/1, attribute_name/1, is_form/1, text/1.

       attribute_arguments(Node::syntaxTree()) -> none | [syntaxTree()]

              Returns the list of argument subtrees  of  an  attribute  node,  if  any.  If  Node
              represents  "-Name.",  the result is none. Otherwise, if Node represents "-Name(E1,
              ..., En).", [E1, ..., E1] is returned.

              See also: attribute/1.

       attribute_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of an attribute node.

              See also: attribute/1.

       binary(Fields::[syntaxTree()]) -> syntaxTree()

              Creates an abstract binary-object template. If Fields is [F1, ..., Fn], the  result
              represents "<<F1, ..., Fn>>".

              See also: binary_field/2, binary_fields/1.

       binary_comp(Template::syntaxTree(), Body::[syntaxTree()]) -> syntaxTree()

              Creates  an  abstract  binary  comprehension.  If Body is [E1, ..., En], the result
              represents "<<Template || E1, ..., En>>".

              See also: binary_comp_body/1, binary_comp_template/1, generator/2.

       binary_comp_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a binary_comp node.

              See also: binary_comp/2.

       binary_comp_template(Node::syntaxTree()) -> syntaxTree()

              Returns the template subtree of a binary_comp node.

              See also: binary_comp/2.

       binary_field(Body) -> syntaxTree()

              Equivalent to binary_field(Body, []).

       binary_field(Body::syntaxTree(), Types::[syntaxTree()]) -> syntaxTree()

              Creates an abstract binary template field. If Types is the empty list,  the  result
              simply  represents  "Body",  otherwise,  if  Types  is  [T1,  ...,  Tn], the result
              represents "Body/T1-...-Tn".

              See   also:   binary/1,   binary_field/1,   binary_field/3,    binary_field_body/1,
              binary_field_size/1, binary_field_types/1.

       binary_field(Body::syntaxTree(), Size, Types::[syntaxTree()]) -> syntaxTree()

              Types:

                 Size = none | syntaxTree()

              Creates  an  abstract binary template field. If Size is none, this is equivalent to
              "binary_field(Body,     Types)",     otherwise     it     is     equivalent      to
              "binary_field(size_qualifier(Body, Size), Types)".

              (This is a utility function.)

              See also: binary/1, binary_field/2, size_qualifier/2.

       binary_field_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a binary_field.

              See also: binary_field/2.

       binary_field_size(Node::syntaxTree()) -> none | syntaxTree()

              Returns  the  size  specifier  subtree  of  a  binary_field  node,  if any. If Node
              represents "Body:Size" or "Body:Size/T1, ..., Tn", the result  is  Size,  otherwise
              none is returned.

              (This is a utility function.)

              See also: binary_field/2, binary_field/3.

       binary_field_types(Node::syntaxTree()) -> [syntaxTree()]

              Returns  the  list  of  type-specifier  subtrees  of  a  binary_field node. If Node
              represents ".../T1, ..., Tn", the result is [T1, ..., Tn], otherwise the result  is
              the empty list.

              See also: binary_field/2.

       binary_fields(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of field subtrees of a binary node.

              See also: binary/1, binary_field/2.

       binary_generator(Pattern::syntaxTree(), Body::syntaxTree()) -> syntaxTree()

              Creates an abstract binary_generator. The result represents "Pattern <- Body".

              See   also:   binary_comp/2,  binary_generator_body/1,  binary_generator_pattern/1,
              list_comp/2.

       binary_generator_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a generator node.

              See also: binary_generator/2.

       binary_generator_pattern(Node::syntaxTree()) -> syntaxTree()

              Returns the pattern subtree of a generator node.

              See also: binary_generator/2.

       block_expr(Body::[syntaxTree()]) -> syntaxTree()

              Creates an abstract block  expression.  If  Body  is  [B1,  ...,  Bn],  the  result
              represents "begin B1, ..., Bn end".

              See also: block_expr_body/1.

       block_expr_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a block_expr node.

              See also: block_expr/1.

       case_expr(Argument::syntaxTree(), Clauses::[syntaxTree()]) -> syntaxTree()

              Creates  an  abstract  case-expression.  If  Clauses  is  [C1, ..., Cn], the result
              represents "case Argument of C1; ...; Cn end". More exactly, if each Ci  represents
              "(Pi)  Gi -> Bi", then the result represents "case Argument of P1 G1 -> B1; ...; Pn
              Gn -> Bn end".

              See  also:  case_expr_argument/1,   case_expr_clauses/1,   clause/3,   cond_expr/1,
              if_expr/1.

       case_expr_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument subtree of a case_expr node.

              See also: case_expr/2.

       case_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of a case_expr node.

              See also: case_expr/2.

       catch_expr(Expr::syntaxTree()) -> syntaxTree()

              Creates an abstract catch-expression. The result represents "catch Expr".

              See also: catch_expr_body/1.

       catch_expr_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a catch_expr node.

              See also: catch_expr/1.

       char(Value::char()) -> syntaxTree()

              Creates  an  abstract  character literal. The result represents "$Name", where Name
              corresponds to Value.

              Note: the literal corresponding to a particular character  value  is  not  uniquely
              defined. E.g., the character "a" can be written both as "$a" and "$\141", and a Tab
              character can be written as "$\11", "$\011" or "$\t".

              See also: char_literal/1, char_value/1, is_char/2.

       char_literal(Node::syntaxTree()) -> string()

              Returns the literal string represented by a char node. This  includes  the  leading
              "$" character.

              See also: char/1.

       char_value(Node::syntaxTree()) -> char()

              Returns the value represented by a char node.

              See also: char/1.

       class_qualifier(Class::syntaxTree(), Body::syntaxTree()) -> syntaxTree()

              Creates an abstract class qualifier. The result represents "Class:Body".

              See also: class_qualifier_argument/1, class_qualifier_body/1, try_expr/4.

       class_qualifier_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument (the class) subtree of a class_qualifier node.

              See also: class_qualifier/2.

       class_qualifier_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a class_qualifier node.

              See also: class_qualifier/2.

       clause(Guard, Body) -> syntaxTree()

              Equivalent to clause([], Guard, Body).

       clause(Patterns::[syntaxTree()], Guard, Body::[syntaxTree()]) -> syntaxTree()

              Types:

                 Guard = none | syntaxTree() | [syntaxTree()] | [[syntaxTree()]]

              Creates an abstract clause. If Patterns is [P1, ..., Pn] and Body is [B1, ..., Bm],
              then if Guard is none, the result represents  "(P1,  ...,  Pn)  ->  B1,  ...,  Bm",
              otherwise,  unless Guard is a list, the result represents "(P1, ..., Pn) when Guard
              -> B1, ..., Bm".

              For simplicity, the Guard argument may also be any of the following:

                * An empty list []. This is equivalent to passing none.

                * A nonempty list [E1, ..., Ej] of syntax trees. This is  equivalent  to  passing
                  conjunction([E1, ..., Ej]).

                * A  nonempty list of lists of syntax trees [[E1_1, ..., E1_k1], ..., [Ej_1, ...,
                  Ej_kj]], which is equivalent to  passing  disjunction([conjunction([E1_1,  ...,
                  E1_k1]), ..., conjunction([Ej_1, ..., Ej_kj])]).

              See also: clause/2, clause_body/1, clause_guard/1, clause_patterns/1.

       clause_body(Node::syntaxTree()) -> [syntaxTree()]

              Return the list of body subtrees of a clause node.

              See also: clause/3.

       clause_guard(Node::syntaxTree()) -> none | syntaxTree()

              Returns  the  guard subtree of a clause node, if any. If Node represents "(P1, ...,
              Pn) when Guard -> B1, ..., Bm", Guard is returned. Otherwise, the result is none.

              See also: clause/3.

       clause_patterns(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of pattern subtrees of a clause node.

              See also: clause/3.

       comment(Strings) -> syntaxTree()

              Equivalent to comment(none, Strings).

       comment(Pad::Padding, Strings::[string()]) -> syntaxTree()

              Types:

                 Padding = none | integer()

              Creates an abstract comment with the given  padding  and  text.  If  Strings  is  a
              (possibly  empty) list ["Txt1", ..., "TxtN"], the result represents the source code
              text

                    %Txt1
                    ...
                    %TxtN

              Padding states the number of empty character positions to the left of  the  comment
              separating  it  horizontally from source code on the same line (if any). If Padding
              is none, a default positive number is used. If Padding is an integer less  than  1,
              there  should be no separating space. Comments are in themselves regarded as source
              program forms.

              See also: comment/1, is_form/1.

       comment_padding(Node::syntaxTree()) -> none | integer()

              Returns the amount of padding before the comment, or none. The latter means that  a
              default padding may be used.

              See also: comment/2.

       comment_text(Node::syntaxTree()) -> [string()]

              Returns the lines of text of the abstract comment.

              See also: comment/2.

       compact_list(Node::syntaxTree()) -> syntaxTree()

              Yields  the  most  compact  form  for  an abstract list skeleton. The result either
              represents "[E1, ..., En | Tail]", where Tail is not a list skeleton, or  otherwise
              simply  "[E1,  ...,  En]".  Annotations  on  subtrees  of  Node that represent list
              skeletons may be lost, but comments will be propagated to the result. Returns  Node
              itself if Node does not represent a list skeleton.

              See also: list/2, normalize_list/1.

       concrete(Node::syntaxTree()) -> term()

              Returns  the Erlang term represented by a syntax tree. Evaluation fails with reason
              badarg if Node does not represent a literal term.

              Note: Currently, the set of syntax trees which have a  concrete  representation  is
              larger  than  the set of trees which can be built using the function abstract/1. An
              abstract character will be concretised as an integer, while abstract/1 does not  at
              present  yield  an  abstract  character  for any input. (Use the char/1 function to
              explicitly create an abstract character.)

              See also: abstract/1, char/1, is_literal/1.

       cond_expr(Clauses::[syntaxTree()]) -> syntaxTree()

              Creates an abstract cond-expression. If  Clauses  is  [C1,  ...,  Cn],  the  result
              represents  "cond  C1;  ...; Cn end". More exactly, if each Ci represents "() Ei ->
              Bi", then the result represents "cond E1 -> B1; ...; En -> Bn end".

              See also: case_expr/2, clause/3, cond_expr_clauses/1.

       cond_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of a cond_expr node.

              See also: cond_expr/1.

       conjunction(List::[syntaxTree()]) -> syntaxTree()

              Creates an abstract conjunction. If List is [E1, ..., En],  the  result  represents
              "E1, ..., En".

              See also: conjunction_body/1, disjunction/1.

       conjunction_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a conjunction node.

              See also: conjunction/1.

       cons(Head::syntaxTree(), Tail::syntaxTree()) -> syntaxTree()

              "Optimising"  list skeleton cons operation. Creates an abstract list skeleton whose
              first element is Head and whose tail  corresponds  to  Tail.  This  is  similar  to
              list([Head],  Tail), except that Tail may not be none, and that the result does not
              necessarily represent exactly "[Head | Tail]", but may depend on the Tail  subtree.
              E.g.,  if  Tail  represents [X, Y], the result may represent "[Head, X, Y]", rather
              than "[Head | [X, Y]]". Annotations on Tail itself may be lost if Tail represents a
              list skeleton, but comments on Tail are propagated to the result.

              See also: list/2, list_head/1, list_tail/1.

       copy_ann(Source::syntaxTree(), Target::syntaxTree()) -> syntaxTree()

              Copies the list of user annotations from Source to Target.

              Note:  this is equivalent to set_ann(Target, get_ann(Source)), but potentially more
              efficient.

              See also: get_ann/1, set_ann/2.

       copy_attrs(Source::syntaxTree(), Target::syntaxTree()) -> syntaxTree()

              Copies the attributes from Source to Target.

              Note: this is equivalent to set_attrs(Target, get_attrs(Source)),  but  potentially
              more efficient.

              See also: get_attrs/1, set_attrs/2.

       copy_comments(Source::syntaxTree(), Target::syntaxTree()) -> syntaxTree()

              Copies the pre- and postcomments from Source to Target.

              Note:    This    is    equivalent    to    set_postcomments(set_precomments(Target,
              get_precomments(Source)),   get_postcomments(Source)),   but    potentially    more
              efficient.

              See  also:  comment/2,  get_postcomments/1,  get_precomments/1, set_postcomments/2,
              set_precomments/2.

       copy_pos(Source::syntaxTree(), Target::syntaxTree()) -> syntaxTree()

              Copies the position information from Source to Target.

              This is  equivalent  to  set_pos(Target,  get_pos(Source)),  but  potentially  more
              efficient.

              See also: get_pos/1, set_pos/2.

       data(Tree::syntaxTree()) -> term()

              For  special  purposes  only.  Returns  the  associated data of a syntax tree node.
              Evaluation fails with reason badarg if is_tree(Node) does not yield true.

              See also: tree/2.

       disjunction(List::[syntaxTree()]) -> syntaxTree()

              Creates an abstract disjunction. If List is [E1, ..., En],  the  result  represents
              "E1; ...; En".

              See also: conjunction/1, disjunction_body/1.

       disjunction_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a disjunction node.

              See also: disjunction/1.

       eof_marker() -> syntaxTree()

              Creates  an  abstract  end-of-file  marker.  This  represents the end of input when
              reading a sequence of source code forms. An end-of-file marker is  itself  regarded
              as a source code form (namely, the last in any sequence in which it occurs). It has
              no defined lexical form.

              Note: this is retained only for backwards compatibility with existing  parsers  and
              tools.

              See also: error_marker/1, is_form/1, warning_marker/1.

       error_marker(Error::term()) -> syntaxTree()

              Creates  an  abstract error marker. The result represents an occurrence of an error
              in the source code, with an associated Erlang  I/O  ErrorInfo  structure  given  by
              Error  (see module io(3erl) for details). Error markers are regarded as source code
              forms, but have no defined lexical form.

              Note: this is supported only for backwards compatibility with existing parsers  and
              tools.

              See also: eof_marker/0, error_marker_info/1, is_form/1, warning_marker/1.

       error_marker_info(Node::syntaxTree()) -> term()

              Returns the ErrorInfo structure of an error_marker node.

              See also: error_marker/1.

       flatten_form_list(Node::syntaxTree()) -> syntaxTree()

              Flattens  sublists  of  a  form_list  node.  Returns Node with all subtrees of type
              form_list recursively expanded, yielding a single "flat" abstract form sequence.

              See also: form_list/1.

       float(Value::float()) -> syntaxTree()

              Creates an abstract floating-point  literal.  The  lexical  representation  is  the
              decimal floating-point numeral of Value.

              See also: float_literal/1, float_value/1.

       float_literal(Node::syntaxTree()) -> string()

              Returns the numeral string represented by a float node.

              See also: float/1.

       float_value(Node::syntaxTree()) -> float()

              Returns  the  value  represented  by  a float node. Note that floating-point values
              should usually not be compared for equality.

              See also: float/1.

       form_list(Forms::[syntaxTree()]) -> syntaxTree()

              Creates an abstract sequence of "source code forms". If Forms  is  [F1,  ...,  Fn],
              where each Fi is a form (cf. is_form/1, the result represents

                    F1
                    ...
                    Fn

              where  the Fi are separated by one or more line breaks. A node of type form_list is
              itself regarded as a source code form; cf. flatten_form_list/1.

              Note: this is simply a way of grouping source code forms as a single  syntax  tree,
              usually in order to form an Erlang module definition.

              See also: flatten_form_list/1, form_list_elements/1, is_form/1.

       form_list_elements(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of subnodes of a form_list node.

              See also: form_list/1.

       fun_expr(Clauses::[syntaxTree()]) -> syntaxTree()

              Creates  an  abstract  fun-expression.  If  Clauses  is  [C1,  ..., Cn], the result
              represents "fun C1; ...; Cn end". More exactly, if each Ci represents  "(Pi1,  ...,
              Pim)  Gi  ->  Bi",  then  the result represents "fun (P11, ..., P1m) G1 -> B1; ...;
              (Pn1, ..., Pnm) Gn -> Bn end".

              See also: fun_expr_arity/1, fun_expr_clauses/1.

       fun_expr_arity(Node::syntaxTree()) -> integer()

              Returns the arity of a fun_expr  node.  The  result  is  the  number  of  parameter
              patterns in the first clause of the fun-expression; subsequent clauses are ignored.

              An  exception  is thrown if fun_expr_clauses(Node) returns an empty list, or if the
              first element of that list is not  a  syntax  tree  C  of  type  clause  such  that
              clause_patterns(C) is a nonempty list.

              See also: clause/3, clause_patterns/1, fun_expr/1, fun_expr_clauses/1.

       fun_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of a fun_expr node.

              See also: fun_expr/1.

       function(Name::syntaxTree(), Clauses::[syntaxTree()]) -> syntaxTree()

              Creates  an  abstract  function definition. If Clauses is [C1, ..., Cn], the result
              represents "Name C1; ...; Name Cn.". More exactly, if  each  Ci  represents  "(Pi1,
              ..., Pim) Gi -> Bi", then the result represents "Name(P11, ..., P1m) G1 -> B1; ...;
              Name(Pn1, ..., Pnm) Gn -> Bn.". Function definitions are source code forms.

              See also: function_arity/1, function_clauses/1, function_name/1, is_form/1, rule/2.

       function_arity(Node::syntaxTree()) -> integer()

              Returns the arity of a function  node.  The  result  is  the  number  of  parameter
              patterns in the first clause of the function; subsequent clauses are ignored.

              An  exception  is thrown if function_clauses(Node) returns an empty list, or if the
              first element of that list is not  a  syntax  tree  C  of  type  clause  such  that
              clause_patterns(C) is a nonempty list.

              See also: clause/3, clause_patterns/1, function/2, function_clauses/1.

       function_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of a function node.

              See also: function/2.

       function_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of a function node.

              See also: function/2.

       generator(Pattern::syntaxTree(), Body::syntaxTree()) -> syntaxTree()

              Creates an abstract generator. The result represents "Pattern <- Body".

              See also: binary_comp/2, generator_body/1, generator_pattern/1, list_comp/2.

       generator_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a generator node.

              See also: generator/2.

       generator_pattern(Node::syntaxTree()) -> syntaxTree()

              Returns the pattern subtree of a generator node.

              See also: generator/2.

       get_ann(Tree::syntaxTree()) -> [term()]

              Returns  the  list  of  user  annotations associated with a syntax tree node. For a
              newly created node, this is the empty list. The annotations may be any terms.

              See also: get_attrs/1, set_ann/2.

       get_attrs(Tree::syntaxTree()) -> syntaxTreeAttributes()

              Returns a representation of the attributes associated with a syntax tree node.  The
              attributes are all the extra information that can be attached to a node. Currently,
              this includes position information, source code comments, and user annotations. The
              result of this function cannot be inspected directly; only attached to another node
              (cf. set_attrs/2).

              For accessing individual attributes, see  get_pos/1,  get_ann/1,  get_precomments/1
              and get_postcomments/1.

              See also: get_ann/1, get_pos/1, get_postcomments/1, get_precomments/1, set_attrs/2.

       get_pos(Node::syntaxTree()) -> term()

              Returns   the  position  information  associated  with  Node.  This  is  usually  a
              nonnegative integer (indicating the source code line number), but may be any  term.
              By  default,  all  new tree nodes have their associated position information set to
              the integer zero.

              See also: get_attrs/1, set_pos/2.

       get_postcomments(Tree::syntaxTree()) -> [syntaxTree()]

              Returns the associated post-comments of a node. This is a possibly  empty  list  of
              abstract  comments,  in  top-down  textual order. When the code is formatted, post-
              comments are typically displayed to  the  right  of  and/or  below  the  node.  For
              example:

                        {foo, X, Y}     % Post-comment of tuple

              If possible, the comment should be moved past any following separator characters on
              the same line, rather than placing the separators on the following line. E.g.:

                        foo([X | Xs], Y) ->
                            foo(Xs, bar(X));     % Post-comment of 'bar(X)' node
                         ...

              (where the comment is moved past the rightmost ")" and the ";").

              See also: comment/2, get_attrs/1, get_precomments/1, set_postcomments/2.

       get_precomments(Tree::syntaxTree()) -> [syntaxTree()]

              Returns the associated pre-comments of a node. This is a  possibly  empty  list  of
              abstract  comments,  in  top-down  textual  order. When the code is formatted, pre-
              comments are typically displayed directly above the node. For example:

                        % Pre-comment of function
                        foo(X) -> {bar, X}.

              If possible, the comment should be moved before any preceding separator  characters
              on the same line. E.g.:

                        foo([X | Xs]) ->
                            % Pre-comment of 'bar(X)' node
                            [bar(X) | foo(Xs)];
                        ...

              (where the comment is moved before the "[").

              See also: comment/2, get_attrs/1, get_postcomments/1, set_precomments/2.

       has_comments(Node::syntaxTree()) -> boolean()

              Yields false if the node has no associated comments, and true otherwise.

              Note:    This    is    equivalent    to    (get_precomments(Node)    ==   [])   and
              (get_postcomments(Node) == []), but potentially more efficient.

              See also: get_postcomments/1, get_precomments/1, remove_comments/1.

       if_expr(Clauses::[syntaxTree()]) -> syntaxTree()

              Creates an abstract  if-expression.  If  Clauses  is  [C1,  ...,  Cn],  the  result
              represents "if C1; ...; Cn end". More exactly, if each Ci represents "() Gi -> Bi",
              then the result represents "if G1 -> B1; ...; Gn -> Bn end".

              See also: case_expr/2, clause/3, if_expr_clauses/1.

       if_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of an if_expr node.

              See also: if_expr/1.

       implicit_fun(Name::syntaxTree()) -> syntaxTree()

              Creates an abstract "implicit fun" expression. The result  represents  "fun  Name".
              Name should represent either F/A or M:F/A

              See  also:  arity_qualifier/2, implicit_fun/2, implicit_fun/3, implicit_fun_name/1,
              module_qualifier/2.

       implicit_fun(Name::syntaxTree(), Arity::syntaxTree()) -> syntaxTree()

              Creates an abstract "implicit fun" expression. If Arity is none, this is equivalent
              to       implicit_fun(Name),      otherwise      it      is      equivalent      to
              implicit_fun(arity_qualifier(Name, Arity)).

              (This is a utility function.)

              See also: implicit_fun/1, implicit_fun/3.

       implicit_fun(Module::syntaxTree(),     Name::syntaxTree(),     Arity::syntaxTree())     ->
       syntaxTree()

              Creates  an abstract module-qualified "implicit fun" expression. If Module is none,
              this is equivalent to implicit_fun(Name, Arity),  otherwise  it  is  equivalent  to
              implicit_fun(module_qualifier(Module, arity_qualifier(Name, Arity)).

              (This is a utility function.)

              See also: implicit_fun/1, implicit_fun/2.

       implicit_fun_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of an implicit_fun node.

              Note:  if  Node represents "fun N/A" or "fun M:N/A", then the result is the subtree
              representing "N/A" or "M:N/A", respectively.

              See also: arity_qualifier/2, implicit_fun/1, module_qualifier/2.

       infix_expr(Left::syntaxTree(),     Operator::syntaxTree(),     Right::syntaxTree())     ->
       syntaxTree()

              Creates an abstract infix operator expression. The result represents "Left Operator
              Right".

              See    also:    infix_expr_left/1,    infix_expr_operator/1,    infix_expr_right/1,
              prefix_expr/2.

       infix_expr_left(Node::syntaxTree()) -> syntaxTree()

              Returns the left argument subtree of an infix_expr node.

              See also: infix_expr/3.

       infix_expr_operator(Node::syntaxTree()) -> syntaxTree()

              Returns the operator subtree of an infix_expr node.

              See also: infix_expr/3.

       infix_expr_right(Node::syntaxTree()) -> syntaxTree()

              Returns the right argument subtree of an infix_expr node.

              See also: infix_expr/3.

       integer(Value::integer()) -> syntaxTree()

              Creates  an  abstract  integer literal. The lexical representation is the canonical
              decimal numeral of Value.

              See also: integer_literal/1, integer_value/1, is_integer/2.

       integer_literal(Node::syntaxTree()) -> string()

              Returns the numeral string represented by an integer node.

              See also: integer/1.

       integer_value(Node::syntaxTree()) -> integer()

              Returns the value represented by an integer node.

              See also: integer/1.

       is_atom(Node::syntaxTree(), Value::atom()) -> boolean()

              Returns true if Node has type atom and represents Value, otherwise false.

              See also: atom/1.

       is_char(Node::syntaxTree(), Value::char()) -> boolean()

              Returns true if Node has type char and represents Value, otherwise false.

              See also: char/1.

       is_form(Node::syntaxTree()) -> boolean()

              Returns true if Node is a syntax tree representing a so-called "source code  form",
              otherwise  false. Forms are the Erlang source code units which, placed in sequence,
              constitute an Erlang program. Current form types are:

              attribute comment error_marker eof_marker form_list
              function rule warning_marker text

              See  also:  attribute/2,  comment/2,  eof_marker/0,  error_marker/1,   form_list/1,
              function/2, rule/2, type/1, warning_marker/1.

       is_integer(Node::syntaxTree(), Value::integer()) -> boolean()

              Returns true if Node has type integer and represents Value, otherwise false.

              See also: integer/1.

       is_leaf(Node::syntaxTree()) -> boolean()

              Returns true if Node is a leaf node, otherwise false. The currently recognised leaf
              node types are:

              atom char comment eof_marker error_marker
              float integer nil operator string
              text underscore variable warning_marker

              A node of type tuple is a leaf node if and only if its arity is zero.

              Note: not all literals are leaf nodes, and vice versa. E.g.,  tuples  with  nonzero
              arity and nonempty lists may be literals, but are not leaf nodes. Variables, on the
              other hand, are leaf nodes but not literals.

              See also: is_literal/1, type/1.

       is_list_skeleton(Node::syntaxTree()) -> boolean()

              Returns true if Node has type list or nil, otherwise false.

              See also: list/2, nil/0.

       is_literal(Node::syntaxTree()) -> boolean()

              Returns true if Node represents a literal  term,  otherwise  false.  This  function
              returns true if and only if the value of concrete(Node) is defined.

              See also: abstract/1, concrete/1.

       is_proper_list(Node::syntaxTree()) -> boolean()

              Returns  true  if Node represents a proper list, and false otherwise. A proper list
              is a list skeleton either on the form "[]" or "[E1, ..., En]", or  "[...  |  Tail]"
              where recursively Tail also represents a proper list.

              Note:  Since Node is a syntax tree, the actual run-time values corresponding to its
              subtrees may often be partially or completely unknown.  Thus,  if  Node  represents
              e.g.  "[...  |  Ns]" (where Ns is a variable), then the function will return false,
              because it is not known whether Ns will be bound to a list  at  run-time.  If  Node
              instead  represents  e.g.  "[1, 2, 3]" or "[A | []]", then the function will return
              true.

              See also: list/2.

       is_string(Node::syntaxTree(), Value::string()) -> boolean()

              Returns true if Node has type string and represents Value, otherwise false.

              See also: string/1.

       is_tree(Tree::syntaxTree()) -> boolean()

              For special purposes only. Returns true if Tree is  an  abstract  syntax  tree  and
              false otherwise.

              Note:  this  function  yields false for all "old-style" erl_parse-compatible "parse
              trees".

              See also: tree/2.

       join_comments(Source::syntaxTree(), Target::syntaxTree()) -> syntaxTree()

              Appends the comments of Source to the current comments of Target.

              Note:   This   is    equivalent    to    add_postcomments(get_postcomments(Source),
              add_precomments(get_precomments(Source), Target)), but potentially more efficient.

              See  also:  add_postcomments/2,  add_precomments/2,  comment/2, get_postcomments/1,
              get_precomments/1.

       list(List) -> syntaxTree()

              Equivalent to list(List, none).

       list(Elements::List, Tail) -> syntaxTree()

              Types:

                 List = [syntaxTree()]
                 Tail = none | syntaxTree()

              Constructs an abstract list skeleton. The result has type list or nil. If List is a
              nonempty  list  [E1, ..., En], the result has type list and represents either "[E1,
              ..., En]", if Tail is none, or otherwise "[E1, ..., En | Tail]".  If  List  is  the
              empty  list,  Tail  must  be  none,  and  in  that case the result has type nil and
              represents "[]" (cf. nil/0).

              The difference between lists as semantic objects (built up of individual "cons" and
              "nil"  terms) and the various syntactic forms for denoting lists may be bewildering
              at first. This module provides functions both for exact control  of  the  syntactic
              representation as well as for the simple composition and deconstruction in terms of
              cons and head/tail operations.

              Note: in list(Elements, none), the "nil" list terminator is  implicit  and  has  no
              associated  information  (cf.  get_attrs/1),  while  in  the  seemingly  equivalent
              list(Elements, Tail) when Tail has type nil, the list terminator subtree  Tail  may
              have attached attributes such as position, comments, and annotations, which will be
              preserved in the result.

              See    also:    compact_list/1,    cons/2,     get_attrs/1,     is_list_skeleton/1,
              is_proper_list/1,     list/1,    list_elements/1,    list_head/1,    list_length/1,
              list_prefix/1, list_suffix/1, list_tail/1, nil/0, normalize_list/1.

       list_comp(Template::syntaxTree(), Body::[syntaxTree()]) -> syntaxTree()

              Creates an abstract list comprehension. If  Body  is  [E1,  ...,  En],  the  result
              represents "[Template || E1, ..., En]".

              See also: generator/2, list_comp_body/1, list_comp_template/1.

       list_comp_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a list_comp node.

              See also: list_comp/2.

       list_comp_template(Node::syntaxTree()) -> syntaxTree()

              Returns the template subtree of a list_comp node.

              See also: list_comp/2.

       list_elements(Node::syntaxTree()) -> [syntaxTree()]

              Returns  the  list  of  element  subtrees of a list skeleton. Node must represent a
              proper  list.  E.g.,  if  Node  represents  "[X1,  X2  |  [X3,  X4  |  []]",   then
              list_elements(Node) yields the list [X1, X2, X3, X4].

              See also: is_proper_list/1, list/2.

       list_head(Node::syntaxTree()) -> syntaxTree()

              Returns  the  head element subtree of a list node. If Node represents "[Head ...]",
              the result will represent "Head".

              See also: cons/2, list/2, list_tail/1.

       list_length(Node::syntaxTree()) -> integer()

              Returns the number of element subtrees of a list skeleton. Node  must  represent  a
              proper  list.  E.g.,  if  Node  represents  "[X1  | [X2, X3 | [X4, X5, X6]]]", then
              list_length(Node) returns the integer 6.

              Note: this is  equivalent  to  length(list_elements(Node)),  but  potentially  more
              efficient.

              See also: is_proper_list/1, list/2, list_elements/1.

       list_prefix(Node::syntaxTree()) -> [syntaxTree()]

              Returns  the  prefix element subtrees of a list node. If Node represents "[E1, ...,
              En]" or "[E1, ..., En | Tail]", the returned value is [E1, ..., En].

              See also: list/2.

       list_suffix(Node::syntaxTree()) -> none | syntaxTree()

              Returns the suffix subtree of a list node, if one exists. If Node represents  "[E1,
              ...,  En  | Tail]", the returned value is Tail, otherwise, i.e., if Node represents
              "[E1, ..., En]", none is returned.

              Note that even if this function returns some Tail that is not  none,  the  type  of
              Tail  can  be nil, if the tail has been given explicitly, and the list skeleton has
              not been compacted (cf. compact_list/1).

              See also: compact_list/1, list/2, nil/0.

       list_tail(Node::syntaxTree()) -> syntaxTree()

              Returns the tail of a list node. If Node represents a  single-element  list  "[E]",
              then the result has type nil, representing "[]". If Node represents "[E1, E2 ...]",
              the result will represent "[E2 ...]", and if Node represents "[Head |  Tail]",  the
              result will represent "Tail".

              See also: cons/2, list/2, list_head/1.

       macro(Name) -> syntaxTree()

              Equivalent to macro(Name, none).

       macro(Name::syntaxTree(), Arguments) -> syntaxTree()

              Types:

                 Arguments = none | [syntaxTree()]

              Creates  an abstract macro application. If Arguments is none, the result represents
              "?Name", otherwise, if Arguments is [A1, ..., An], the result represents "?Name(A1,
              ..., An)".

              Notes:  if  Arguments  is the empty list, the result will thus represent "?Name()",
              including a pair of matching parentheses.

              The only syntactical limitation imposed by the preprocessor on the arguments  to  a
              macro  application  (viewed  as  sequences of tokens) is that they must be balanced
              with respect to parentheses, brackets, begin ... end, case ... end, etc.  The  text
              node  type  can  be  used  to  represent  arguments  which  are  not regular Erlang
              constructs.

              See also: macro/1, macro_arguments/1, macro_name/1, text/1.

       macro_arguments(Node::syntaxTree()) -> none | [syntaxTree()]

              Returns the list of argument subtrees of a macro node, if any. If  Node  represents
              "?Name", none is returned. Otherwise, if Node represents "?Name(A1, ..., An)", [A1,
              ..., An] is returned.

              See also: macro/2.

       macro_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of a macro node.

              See also: macro/2.

       make_tree(Type::atom(), Groups::[[syntaxTree()]]) -> syntaxTree()

              Creates a syntax tree with the given type and subtrees. Type must be  a  node  type
              name  (cf.  type/1)  that  does not denote a leaf node type (cf. is_leaf/1). Groups
              must be a nonempty list of groups of syntax trees, representing the subtrees  of  a
              node  of  the given type, in left-to-right order as they would occur in the printed
              program text, grouped by category as done by subtrees/1.

              The  result  of  copy_attrs(Node,   make_tree(type(Node),   subtrees(Node)))   (cf.
              update_tree/2)  represents the same source code text as the original Node, assuming
              that subtrees(Node) yields a nonempty list. However, it does not  necessarily  have
              the same data representation as Node.

              See also: copy_attrs/2, is_leaf/1, subtrees/1, type/1, update_tree/2.

       match_expr(Pattern::syntaxTree(), Body::syntaxTree()) -> syntaxTree()

              Creates an abstract match-expression. The result represents "Pattern = Body".

              See also: match_expr_body/1, match_expr_pattern/1.

       match_expr_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a match_expr node.

              See also: match_expr/2.

       match_expr_pattern(Node::syntaxTree()) -> syntaxTree()

              Returns the pattern subtree of a match_expr node.

              See also: match_expr/2.

       meta(Tree::syntaxTree()) -> syntaxTree()

              Creates  a  meta-representation  of  a syntax tree. The result represents an Erlang
              expression  "MetaTree"  which,  if  evaluated,  will  yield  a  new   syntax   tree
              representing  the  same  source  code  text  as  Tree  (although  the  actual  data
              representation may  be  different).  The  expression  represented  by  MetaTree  is
              implementation  independent with regard to the data structures used by the abstract
              syntax tree implementation. Comments attached to nodes of Tree will  be  preserved,
              but other attributes are lost.

              Any  node  in  Tree  whose  node  type  is variable (cf. type/1), and whose list of
              annotations (cf. get_ann/1) contains the atom meta_var, will  remain  unchanged  in
              the  resulting tree, except that exactly one occurrence of meta_var is removed from
              its annotation list.

              The main use of the function meta/1 is to transform a data  structure  Tree,  which
              represents  a piece of program code, into a form that is representation independent
              when printed. E.g., suppose Tree represents a variable named "V". Then (assuming  a
              function  print/1  for  printing  syntax trees), evaluating print(abstract(Tree)) -
              simply using abstract/1 to map  the  actual  data  structure  onto  a  syntax  tree
              representation  -  would  output  a  string  that might look something like "{tree,
              variable, ..., "V", ...}", which is obviously dependent on  the  implementation  of
              the abstract syntax trees. This could e.g. be useful for caching a syntax tree in a
              file. However, in some situations like in a program generator generator  (with  two
              "generator"),  it may be unacceptable. Using print(meta(Tree)) instead would output
              a representation independent syntax tree generating expression; in the above  case,
              something like "erl_syntax:variable("V")".

              See also: abstract/1, get_ann/1, type/1.

       module_qualifier(Module::syntaxTree(), Body::syntaxTree()) -> syntaxTree()

              Creates an abstract module qualifier. The result represents "Module:Body".

              See also: module_qualifier_argument/1, module_qualifier_body/1.

       module_qualifier_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument (the module) subtree of a module_qualifier node.

              See also: module_qualifier/2.

       module_qualifier_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a module_qualifier node.

              See also: module_qualifier/2.

       nil() -> syntaxTree()

              Creates  an  abstract  empty  list.  The  result represents "[]". The empty list is
              traditionally called "nil".

              See also: is_list_skeleton/1, list/2.

       normalize_list(Node::syntaxTree()) -> syntaxTree()

              Expands an abstract list skeleton to its most explicit  form.  If  Node  represents
              "[E1, ..., En | Tail]", the result represents "[E1 | ... [En | Tail1] ... ]", where
              Tail1 is the result of normalize_list(Tail). If Node represents  "[E1,  ...,  En]",
              the  result  simply  represents  "[E1  |  ...  [En  |  []] ... ]". If Node does not
              represent a list skeleton, Node itself is returned.

              See also: compact_list/1, list/2.

       operator(Name) -> syntaxTree()

              Types:

                 Name = atom() | string()

              Creates an abstract operator. The name of the operator is  the  character  sequence
              represented  by  Name.  This  is  analogous  to  the  print name of an atom, but an
              operator is never written within single-quotes; e.g., the result of  operator('++')
              represents "++" rather than "'++'".

              See also: atom/1, operator_literal/1, operator_name/1.

       operator_literal(Node::syntaxTree()) -> string()

              Returns  the  literal  string  represented  by an operator node. This is simply the
              operator name as a string.

              See also: operator/1.

       operator_name(Node::syntaxTree()) -> atom()

              Returns the name of an operator node. Note that the name is returned as an atom.

              See also: operator/1.

       parentheses(Body::syntaxTree()) -> syntaxTree()

              Creates an abstract  parenthesised  expression.  The  result  represents  "(Body)",
              independently of the context.

              See also: parentheses_body/1.

       parentheses_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a parentheses node.

              See also: parentheses/1.

       prefix_expr(Operator::syntaxTree(), Argument::syntaxTree()) -> syntaxTree()

              Creates  an  abstract  prefix  operator expression. The result represents "Operator
              Argument".

              See also: infix_expr/3, prefix_expr_argument/1, prefix_expr_operator/1.

       prefix_expr_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument subtree of a prefix_expr node.

              See also: prefix_expr/2.

       prefix_expr_operator(Node::syntaxTree()) -> syntaxTree()

              Returns the operator subtree of a prefix_expr node.

              See also: prefix_expr/2.

       qualified_name(Segments::[syntaxTree()]) -> syntaxTree()

              Creates an abstract qualified name. The result  represents  "S1.S2.  ...  .Sn",  if
              Segments is [S1, S2, ..., Sn].

              See also: qualified_name_segments/1.

       qualified_name_segments(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of name segments of a qualified_name node.

              See also: qualified_name/1.

       query_expr(Body::syntaxTree()) -> syntaxTree()

              Creates  an  abstract Mnemosyne query expression. The result represents "query Body
              end".

              See also: query_expr_body/1, record_access/2, rule/2.

       query_expr_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a query_expr node.

              See also: query_expr/1.

       receive_expr(Clauses) -> syntaxTree()

              Equivalent to receive_expr(Clauses, none, []).

       receive_expr(Clauses::[syntaxTree()], Timeout, Action::[syntaxTree()]) -> syntaxTree()

              Types:

                 Timeout = none | syntaxTree()

              Creates an abstract receive-expression. If Timeout is none, the  result  represents
              "receive  C1;  ...; Cn end" (the Action argument is ignored). Otherwise, if Clauses
              is [C1, ..., Cn] and Action is [A1, ..., Am], the result  represents  "receive  C1;
              ...;  Cn  after  Timeout  ->  A1, ..., Am end". More exactly, if each Ci represents
              "(Pi) Gi -> Bi", then the result represents "receive P1 G1 -> B1; ...; Pn Gn ->  Bn
              ... end".

              Note  that  in  Erlang,  a  receive-expression  must have at least one clause if no
              timeout part is specified.

              See   also:   case_expr/2,   clause/3,    receive_expr/1,    receive_expr_action/1,
              receive_expr_clauses/1, receive_expr_timeout/1.

       receive_expr_action(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of action body subtrees of a receive_expr node. If Node represents
              "receive C1; ...; Cn end", this is the empty list.

              See also: receive_expr/3.

       receive_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Types:

                 receive_expr

              Returns the list of clause subtrees of a receive_expr node.

              See also: receive_expr/3.

       receive_expr_timeout(Node::syntaxTree()) -> Timeout

              Types:

                 Timeout = none | syntaxTree()

              Returns the timeout subtree of a receive_expr node,  if  any.  If  Node  represents
              "receive C1; ...; Cn end", none is returned. Otherwise, if Node represents "receive
              C1; ...; Cn after Timeout -> ... end", Timeout is returned.

              See also: receive_expr/3.

       record_access(Argument, Field) -> syntaxTree()

              Equivalent to record_access(Argument, none, Field).

       record_access(Argument::syntaxTree(), Type, Field::syntaxTree()) -> syntaxTree()

              Types:

                 Type = none | syntaxTree()

              Creates an abstract record field access expression. If Type is not none, the result
              represents "Argument#Type.Field".

              If  Type  is  none,  the result represents "Argument.Field". This is a special form
              only allowed within Mnemosyne queries.

              See     also:     query_expr/1,     record_access/2,      record_access_argument/1,
              record_access_field/1, record_access_type/1, record_expr/3.

       record_access_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument subtree of a record_access node.

              See also: record_access/3.

       record_access_field(Node::syntaxTree()) -> syntaxTree()

              Returns the field subtree of a record_access node.

              See also: record_access/3.

       record_access_type(Node::syntaxTree()) -> none | syntaxTree()

              Returns  the  type  subtree  of  a  record_access  node, if any. If Node represents
              "Argument.Field",   none   is    returned,    otherwise    if    Node    represents
              "Argument#Type.Field", Type is returned.

              See also: record_access/3.

       record_expr(Type, Fields) -> syntaxTree()

              Equivalent to record_expr(none, Type, Fields).

       record_expr(Argument, Type::syntaxTree(), Fields::[syntaxTree()]) -> syntaxTree()

              Types:

                 Argument = none | syntaxTree()

              Creates an abstract record expression. If Fields is [F1, ..., Fn], then if Argument
              is none, the result  represents  "#Type{F1,  ...,  Fn}",  otherwise  it  represents
              "Argument#Type{F1, ..., Fn}".

              See      also:      record_access/3,     record_expr/2,     record_expr_argument/1,
              record_expr_fields/1, record_expr_type/1, record_field/2, record_index_expr/2.

       record_expr_argument(Node::syntaxTree()) -> none | syntaxTree()

              Returns the argument subtree of a record_expr node,  if  any.  If  Node  represents
              "#Type{...}", none is returned. Otherwise, if Node represents "Argument#Type{...}",
              Argument is returned.

              See also: record_expr/3.

       record_expr_fields(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of field subtrees of a record_expr node.

              See also: record_expr/3.

       record_expr_type(Node::syntaxTree()) -> syntaxTree()

              Returns the type subtree of a record_expr node.

              See also: record_expr/3.

       record_field(Name) -> syntaxTree()

              Equivalent to record_field(Name, none).

       record_field(Name::syntaxTree(), Value) -> syntaxTree()

              Types:

                 Value = none | syntaxTree()

              Creates an abstract record field  specification.  If  Value  is  none,  the  result
              represents simply "Name", otherwise it represents "Name = Value".

              See also: record_expr/3, record_field_name/1, record_field_value/1.

       record_field_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of a record_field node.

              See also: record_field/2.

       record_field_value(Node::syntaxTree()) -> none | syntaxTree()

              Returns  the  value  subtree  of  a  record_field  node, if any. If Node represents
              "Name", none is returned. Otherwise, if Node represents "Name =  Value",  Value  is
              returned.

              See also: record_field/2.

       record_index_expr(Type::syntaxTree(), Field::syntaxTree()) -> syntaxTree()

              Creates   an   abstract  record  field  index  expression.  The  result  represents
              "#Type.Field".

              (Note: the function name record_index/2 is reserved by the Erlang  compiler,  which
              is why that name could not be used for this constructor.)

              See also: record_expr/3, record_index_expr_field/1, record_index_expr_type/1.

       record_index_expr_field(Node::syntaxTree()) -> syntaxTree()

              Returns the field subtree of a record_index_expr node.

              See also: record_index_expr/2.

       record_index_expr_type(Node::syntaxTree()) -> syntaxTree()

              Returns the type subtree of a record_index_expr node.

              See also: record_index_expr/2.

       remove_comments(Node::syntaxTree()) -> syntaxTree()

              Clears the associated comments of Node.

              Note:  This  is  equivalent to set_precomments(set_postcomments(Node, []), []), but
              potentially more efficient.

              See also: set_postcomments/2, set_precomments/2.

       revert(Tree::syntaxTree()) -> syntaxTree()

              Returns an erl_parse-compatible representation of a syntax tree,  if  possible.  If
              Tree  represents  a well-formed Erlang program or expression, the conversion should
              work without problems. Typically, is_tree/1 yields true if conversion failed (i.e.,
              the result is still an abstract syntax tree), and false otherwise.

              The  is_tree/1 test is not completely foolproof. For a few special node types (e.g.
              arity_qualifier), if such a node occurs in a context where it is not  expected,  it
              will  be  left  unchanged  as  a  non-reverted subtree of the result. This can only
              happen if Tree does not actually represent legal Erlang code.

              See also: erl_parse(3erl), revert_forms/1.

       revert_forms(L::Forms) -> [erl_parse()]

              Types:

                 Forms = syntaxTree() | [syntaxTree()]

              Reverts a sequence of Erlang source code forms. The sequence can be given either as
              a  form_list  syntax  tree (possibly nested), or as a list of "program form" syntax
              trees. If successful, the corresponding flat list  of  erl_parse-compatible  syntax
              trees  is  returned  (cf.  revert/1).  If  some program form could not be reverted,
              {error, Form} is thrown. Standalone comments in the form sequence are discarded.

              See also: form_list/1, is_form/1, revert/1.

       rule(Name::syntaxTree(), Clauses::[syntaxTree()]) -> syntaxTree()

              Creates an abstract Mnemosyne rule. If  Clauses  is  [C1,  ...,  Cn],  the  results
              represents  "Name  C1;  ...;  Name Cn.". More exactly, if each Ci represents "(Pi1,
              ..., Pim) Gi -> Bi", then the result represents "Name(P11, ..., P1m) G1 :- B1; ...;
              Name(Pn1, ..., Pnm) Gn :- Bn.". Rules are source code forms.

              See also: function/2, is_form/1, rule_arity/1, rule_clauses/1, rule_name/1.

       rule_arity(Node::syntaxTree()) -> integer()

              Returns the arity of a rule node. The result is the number of parameter patterns in
              the first clause of the rule; subsequent clauses are ignored.

              An exception is thrown if rule_clauses(Node) returns an empty list, or if the first
              element   of  that  list  is  not  a  syntax  tree  C  of  type  clause  such  that
              clause_patterns(C) is a nonempty list.

              See also: clause/3, clause_patterns/1, rule/2, rule_clauses/1.

       rule_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of clause subtrees of a rule node.

              See also: rule/2.

       rule_name(Node::syntaxTree()) -> syntaxTree()

              Returns the name subtree of a rule node.

              See also: rule/2.

       set_ann(Node::syntaxTree(), Annotations::[term()]) -> syntaxTree()

              Sets the list of user annotations of Node to Annotations.

              See also: add_ann/2, copy_ann/2, get_ann/1.

       set_attrs(Node::syntaxTree(), Attributes::syntaxTreeAttributes()) -> syntaxTree()

              Sets the attributes of Node to Attributes.

              See also: copy_attrs/2, get_attrs/1.

       set_pos(Node::syntaxTree(), Pos::term()) -> syntaxTree()

              Sets the position information of Node to Pos.

              See also: copy_pos/2, get_pos/1.

       set_postcomments(Node::syntaxTree(), Comments::[syntaxTree()]) -> syntaxTree()

              Sets the post-comments of Node to Comments. Comments should  be  a  possibly  empty
              list of abstract comments, in top-down textual order

              See   also:  add_postcomments/2,  comment/2,  copy_comments/2,  get_postcomments/1,
              join_comments/2, remove_comments/1, set_precomments/2.

       set_precomments(Node::syntaxTree(), Comments::[syntaxTree()]) -> syntaxTree()

              Sets the pre-comments of Node to Comments. Comments should be a possibly empty list
              of abstract comments, in top-down textual order.

              See   also:   add_precomments/2,   comment/2,  copy_comments/2,  get_precomments/1,
              join_comments/2, remove_comments/1, set_postcomments/2.

       size_qualifier(Body::syntaxTree(), Size::syntaxTree()) -> syntaxTree()

              Creates an abstract size qualifier. The result represents "Body:Size".

              See also: size_qualifier_argument/1, size_qualifier_body/1.

       size_qualifier_argument(Node::syntaxTree()) -> syntaxTree()

              Returns the argument subtree (the size) of a size_qualifier node.

              See also: size_qualifier/2.

       size_qualifier_body(Node::syntaxTree()) -> syntaxTree()

              Returns the body subtree of a size_qualifier node.

              See also: size_qualifier/2.

       string(Value::string()) -> syntaxTree()

              Creates an abstract string literal. The result  represents  "Text"  (including  the
              surrounding double-quotes), where Text corresponds to the sequence of characters in
              Value, but not  representing  a  specific  string  literal.  E.g.,  the  result  of
              string("x\ny") represents any and all of "x\ny", "x\12y", "x\012y" and "x\^Jy"; cf.
              char/1.

              See also: char/1, is_string/2, string_literal/1, string_value/1.

       string_literal(Node::syntaxTree()) -> string()

              Returns the literal string represented by a string node. This includes  surrounding
              double-quote characters.

              See also: string/1.

       string_value(Node::syntaxTree()) -> string()

              Returns the value represented by a string node.

              See also: string/1.

       subtrees(Node::syntaxTree()) -> [[syntaxTree()]]

              Returns  the  grouped list of all subtrees of a syntax tree. If Node is a leaf node
              (cf. is_leaf/1), this is the empty list, otherwise the result is always a  nonempty
              list,  containing  the  lists  of  subtrees of Node, in left-to-right order as they
              occur in the printed program text, and  grouped  by  category.  Often,  each  group
              contains only a single subtree.

              Depending  on  the type of Node, the size of some groups may be variable (e.g., the
              group consisting of all the elements of a tuple), while others always  contain  the
              same  number  of  elements  -  usually  exactly one (e.g., the group containing the
              argument expression of a case-expression). Note, however, that the exact  structure
              of  the  returned  list  (for  a given node type) should in general not be depended
              upon, since it might be subject to change without notice.

              The function subtrees/1 and the constructor functions make_tree/2 and update_tree/2
              can  be  a  great  help  if  one  wants to traverse a syntax tree, visiting all its
              subtrees, but treat nodes of the tree in a uniform way in most or all cases.  Using
              these  functions  makes  this simple, and also assures that your code is not overly
              sensitive to extensions of the syntax tree data type, because any  node  types  not
              explicitly handled by your code can be left to a default case.

              For example:

                  postorder(F, Tree) ->
                      F(case subtrees(Tree) of
                          [] -> Tree;
                          List -> update_tree(Tree,
                                              [[postorder(F, Subtree)
                                                || Subtree <- Group]
                                               || Group <- List])
                        end).

              maps  the  function F on Tree and all its subtrees, doing a post-order traversal of
              the syntax tree. (Note the use of update_tree/2 to preserve node attributes.) For a
              simple function like:

                  f(Node) ->
                      case type(Node) of
                          atom -> atom("a_" ++ atom_name(Node));
                          _ -> Node
                      end.

              the  call postorder(fun f/1, Tree) will yield a new representation of Tree in which
              all atom names have been extended with the prefix "a_", but nothing else (including
              comments, annotations and line numbers) has been changed.

              See also: copy_attrs/2, is_leaf/1, make_tree/2, type/1.

       text(String::string()) -> syntaxTree()

              Creates  an  abstract  piece of source code text. The result represents exactly the
              sequence of characters in String. This is useful  in  cases  when  one  wants  full
              control of the resulting output, e.g., for the appearance of floating-point numbers
              or macro definitions.

              See also: text_string/1.

       text_string(Node::syntaxTree()) -> string()

              Returns the character sequence represented by a text node.

              See also: text/1.

       tree(Type) -> syntaxTree()

              Equivalent to tree(Type, []).

       tree(Type::atom(), Data::term()) -> syntaxTree()

              For special purposes only. Creates an abstract syntax tree node with type tag  Type
              and associated data Data.

              This  function and the related is_tree/1 and data/1 provide a uniform way to extend
              the set of erl_parse node types. The associated data is any term, whose format  may
              depend on the type tag.

              Notes:

                * Any  nodes  created  outside  of  this module must have type tags distinct from
                  those currently defined by this module; see type/1 for a complete list.

                * The type tag of a syntax tree node may also be used as a  primary  tag  by  the
                  erl_parse  representation;  in  that case, the selector functions for that node
                  type must handle both the abstract syntax tree  and  the  erl_parse  form.  The
                  function  type(T)  should  return  the  correct  type  tag  regardless  of  the
                  representation of T, so that the user sees no difference between erl_syntax and
                  erl_parse nodes.

              See also: data/1, is_tree/1, type/1.

       try_after_expr(Body::syntaxTree(), After::[syntaxTree()]) -> syntaxTree()

              Equivalent to try_expr(Body, [], [], After).

       try_expr(Body::syntaxTree(), Handlers::[syntaxTree()]) -> syntaxTree()

              Equivalent to try_expr(Body, [], Handlers).

       try_expr(Body::syntaxTree(),    Clauses::[syntaxTree()],    Handlers::[syntaxTree()])   ->
       syntaxTree()

              Equivalent to try_expr(Body, Clauses, Handlers, []).

       try_expr(Body::[syntaxTree()],     Clauses::[syntaxTree()],      Handlers::[syntaxTree()],
       After::[syntaxTree()]) -> syntaxTree()

              Creates  an abstract try-expression. If Body is [B1, ..., Bn], Clauses is [C1, ...,
              Cj], Handlers is [H1, ..., Hk], and After is [A1, ..., Am], the  result  represents
              "try  B1,  ...,  Bn  of  C1; ...; Cj catch H1; ...; Hk after A1, ..., Am end". More
              exactly, if each Ci represents "(CPi) CGi -> CBi", and each  Hi  represents  "(HPi)
              HGi  ->  HBi",  then the result represents "try B1, ..., Bn of CP1 CG1 -> CB1; ...;
              CPj CGj -> CBj catch HP1 HG1 -> HB1; ...; HPk HGk -> HBk after A1,  ...,  Am  end";
              cf.  case_expr/2.  If Clauses is the empty list, the of ... section is left out. If
              After is the empty list, the after ... section is left  out.  If  Handlers  is  the
              empty list, and After is nonempty, the catch ... section is left out.

              See  also:  case_expr/2, class_qualifier/2, clause/3, try_after_expr/2, try_expr/2,
              try_expr/3,      try_expr_after/1,       try_expr_body/1,       try_expr_clauses/1,
              try_expr_handlers/1.

       try_expr_after(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of "after" subtrees of a try_expr node.

              See also: try_expr/4.

       try_expr_body(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of body subtrees of a try_expr node.

              See also: try_expr/4.

       try_expr_clauses(Node::syntaxTree()) -> [syntaxTree()]

              Returns  the  list  of  case-clause subtrees of a try_expr node. If Node represents
              "try Body catch H1; ...; Hn end", the result is the empty list.

              See also: try_expr/4.

       try_expr_handlers(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of handler-clause subtrees of a try_expr node.

              See also: try_expr/4.

       tuple(Elements::[syntaxTree()]) -> syntaxTree()

              Creates an abstract tuple. If Elements is [X1,  ...,  Xn],  the  result  represents
              "{X1, ..., Xn}".

              Note:  The Erlang language has distinct 1-tuples, i.e., {X} is always distinct from
              X itself.

              See also: tuple_elements/1, tuple_size/1.

       tuple_elements(Node::syntaxTree()) -> [syntaxTree()]

              Returns the list of element subtrees of a tuple node.

              See also: tuple/1.

       tuple_size(Node::syntaxTree()) -> integer()

              Returns the number of elements of a tuple node.

              Note: this is equivalent  to  length(tuple_elements(Node)),  but  potentially  more
              efficient.

              See also: tuple/1, tuple_elements/1.

       type(Node::syntaxTree()) -> atom()

              Returns  the type tag of Node. If Node does not represent a syntax tree, evaluation
              fails with reason badarg. Node types currently defined by this module are:

              application arity_qualifier atom attribute
              binary binary_field block_expr case_expr
              catch_expr char class_qualifier clause
              comment cond_expr conjunction disjunction
              eof_marker error_marker float form_list
              fun_expr function generator if_expr
              implicit_fun infix_expr integer list
              list_comp macro match_expr module_qualifier
              nil operator parentheses prefix_expr
              qualified_name query_expr receive_expr record_access
              record_expr record_field record_index_expr rule
              size_qualifier string text try_expr
              tuple underscore variable warning_marker

              The user may (for special purposes) create additional nodes with other  type  tags,
              using the tree/2 function.

              Note: The primary constructor functions for a node type should always have the same
              name as the node type itself.

              See  also:  application/3,  arity_qualifier/2,   atom/1,   attribute/2,   binary/1,
              binary_field/2, block_expr/1, case_expr/2, catch_expr/1, char/1, class_qualifier/2,
              clause/3,  comment/2,  cond_expr/1,  conjunction/1,  disjunction/1,   eof_marker/0,
              error_marker/1,   float/1,   form_list/1,   fun_expr/1,   function/2,  generator/2,
              if_expr/1, implicit_fun/2, infix_expr/3, integer/1, list/2,  list_comp/2,  macro/2,
              match_expr/2,  module_qualifier/2, nil/0, operator/1, parentheses/1, prefix_expr/2,
              qualified_name/1,  query_expr/1,  receive_expr/3,  record_access/3,  record_expr/2,
              record_field/2,  record_index_expr/2,  rule/2,  size_qualifier/2, string/1, text/1,
              tree/2, try_expr/3, tuple/1, underscore/0, variable/1, warning_marker/1.

       underscore() -> syntaxTree()

              Creates an abstract universal pattern ("_"). The lexical representation is a single
              underscore character. Note that this is not a variable, lexically speaking.

              See also: variable/1.

       update_tree(Node::syntaxTree(), Groups::[[syntaxTree()]]) -> syntaxTree()

              Creates  a syntax tree with the same type and attributes as the given tree. This is
              equivalent to copy_attrs(Node, make_tree(type(Node), Groups)).

              See also: copy_attrs/2, make_tree/2, type/1.

       variable(Name) -> syntaxTree()

              Types:

                 Name = atom() | string()

              Creates an abstract variable with the given name. Name may be any  atom  or  string
              that  represents  a  lexically  valid  variable  name,  but not a single underscore
              character; cf. underscore/0.

              Note: no checking is done  whether  the  character  sequence  represents  a  proper
              variable  name,  i.e.,  whether  or  not its first character is an uppercase Erlang
              character, or whether it does not contain control characters, whitespace, etc.

              See also: underscore/0, variable_literal/1, variable_name/1.

       variable_literal(Node::syntaxTree()) -> string()

              Returns the name of a variable node as a string.

              See also: variable/1.

       variable_name(Node::syntaxTree()) -> atom()

              Returns the name of a variable node as an atom.

              See also: variable/1.

       warning_marker(Error::term()) -> syntaxTree()

              Creates an abstract warning marker.  The  result  represents  an  occurrence  of  a
              possible  problem  in  the  source  code,  with  an associated Erlang I/O ErrorInfo
              structure given by Error (see module io(3erl) for  details).  Warning  markers  are
              regarded as source code forms, but have no defined lexical form.

              Note:  this is supported only for backwards compatibility with existing parsers and
              tools.

              See also: eof_marker/0, error_marker/1, is_form/1, warning_marker_info/1.

       warning_marker_info(Node::syntaxTree()) -> term()

              Returns the ErrorInfo structure of a warning_marker node.

              See also: warning_marker/1.

AUTHORS

       Richard Carlsson <richardc@it.uu.se>

                                       syntax_tools 1.6.7.1                      erl_syntax(3erl)