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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())

              The optional argument HookFunction, shown in the functions described below, defines
              a  function  which  is  called  when an unknown form occurs where there should be a
              valid expression.

              If HookFunction is equal to none there is no hook function.

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

              If CurrentIndentation is negative, there will be 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

       form(Form) -> io_lib:chars()

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

              Types:

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

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

       attribute(Attribute) -> io_lib:chars()

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

              Types:

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

              The same as form, but only for the attribute Attribute.

       function(Function) -> io_lib:chars()

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

              Types:

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

              The same as form, but only for the function Function.

       guard(Guard) -> io_lib:chars()

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

              Types:

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

              The same as form, but only for the guard test Guard.

       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()

              The same as form, but only for the sequence of expressions in Expressions.

       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()

              This  function  prints  one  expression.  It  is useful for implementing hooks (see
              below).

BUGS

       It should be possible to have hook functions  for  unknown  forms  at  places  other  than
       expressions.

SEE ALSO

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