NAME

       erl_pp - The Erlang pretty printer.

DESCRIPTION

       The functions in this module are used to generate aesthetically attractive representations
       of abstract forms, which are suitable for printing. All functions return  (possibly  deep)
       lists of characters and generate an error if the form is wrong.

       All  functions  can have an optional argument, which specifies a hook that is called if an
       attempt is made to print an unknown form.

DATA TYPES

       hook_function() =
           none |
           fun((Expr :: erl_parse:abstract_expr(),
                CurrentIndentation :: integer(),
                CurrentPrecedence :: integer() >= 0,
                Options :: options()) ->
                   io_lib:chars())

              Optional argument HookFunction, shown in the functions described  in  this  module,
              defines  a function that is called when an unknown form occurs where there is to be
              a valid expression. If HookFunction is equal to none, there is no hook function.

              The called hook function is  to  return  a  (possibly  deep)  list  of  characters.
              Function expr/4 is useful in a hook.

              If  CurrentIndentation  is  negative,  there are no line breaks and only a space is
              used as a separator.

       option() =
           {hook, hook_function()} |
           {encoding, latin1 | unicode | utf8} |
           {quote_singleton_atom_types, boolean()}

              The option quote_singleton_atom_types is used to add quotes to all  singleton  atom
              types.

       options() = hook_function() | [option()]

EXPORTS

       attribute(Attribute) -> io_lib:chars()

       attribute(Attribute, Options) -> io_lib:chars()

              Types:

                 Attribute = erl_parse:abstract_form()
                 Options = options()

              Same as form/1,2, but only for attribute Attribute.

       expr(Expression) -> io_lib:chars()

       expr(Expression, Options) -> io_lib:chars()

       expr(Expression, Indent, Options) -> io_lib:chars()

       expr(Expression, Indent, Precedence, Options) -> io_lib:chars()

              Types:

                 Expression = erl_parse:abstract_expr()
                 Indent = integer()
                 Precedence = integer() >= 0
                 Options = options()

              Prints  one  expression.  It  is  useful  for implementing hooks (see section Known
              Limitations).

       exprs(Expressions) -> io_lib:chars()

       exprs(Expressions, Options) -> io_lib:chars()

       exprs(Expressions, Indent, Options) -> io_lib:chars()

              Types:

                 Expressions = [erl_parse:abstract_expr()]
                 Indent = integer()
                 Options = options()

              Same as form/1,2, but only for the sequence of expressions in Expressions.

       form(Form) -> io_lib:chars()

       form(Form, Options) -> io_lib:chars()

              Types:

                 Form = erl_parse:abstract_form() | erl_parse:form_info()
                 Options = options()

              Pretty prints a Form, which is an abstract form of  a  type  that  is  returned  by
              erl_parse:parse_form/1.

       function(Function) -> io_lib:chars()

       function(Function, Options) -> io_lib:chars()

              Types:

                 Function = erl_parse:abstract_form()
                 Options = options()

              Same as form/1,2, but only for function Function.

       guard(Guard) -> io_lib:chars()

       guard(Guard, Options) -> io_lib:chars()

              Types:

                 Guard = [erl_parse:abstract_expr()]
                 Options = options()

              Same as form/1,2, but only for the guard test Guard.

KNOWN LIMITATIONS

       It  is  not  possible  to  have  hook  functions  for  unknown  forms at other places than
       expressions.

SEE ALSO

       erl_eval(3erl), erl_parse(3erl), io(3erl)