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}

       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)