.TH erl_pp 3erl "stdlib 3.2" "Ericsson AB" "Erlang Module Definition"
.SH NAME
erl_pp \- The Erlang pretty printer.
.SH DESCRIPTION
.LP
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\&.
.LP
All functions can have an optional argument, which specifies a hook that is called if an attempt is made to print an unknown form\&.
.SH DATA TYPES
.nf

\fBhook_function()\fR\& = 
.br
    none |
.br
    fun((Expr :: \fBerl_parse:abstract_expr()\fR\&,
.br
         CurrentIndentation :: integer(),
.br
         CurrentPrecedence :: integer() >= 0,
.br
         Options :: \fBoptions()\fR\&) ->
.br
            \fBio_lib:chars()\fR\&)
.br
.fi
.RS
.LP
Optional argument \fIHookFunction\fR\&, 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 \fIHookFunction\fR\& is equal to \fInone\fR\&, there is no hook function\&.
.LP
The called hook function is to return a (possibly deep) list of characters\&. Function \fB\fIexpr/4\fR\&\fR\& is useful in a hook\&.
.LP
If \fICurrentIndentation\fR\& is negative, there are no line breaks and only a space is used as a separator\&.
.RE

.nf

\fBoption()\fR\& = 
.br
    {hook, \fBhook_function()\fR\&} | {encoding, latin1 | unicode | utf8}
.br
.fi
.nf

\fBoptions()\fR\& = \fBhook_function()\fR\& | [\fBoption()\fR\&]
.br
.fi
.SH EXPORTS
.LP
.nf

.B
attribute(Attribute) -> io_lib:chars()
.br
.fi
.br
.nf

.B
attribute(Attribute, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Attribute = \fBerl_parse:abstract_form()\fR\&
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Same as \fB\fIform/1,2\fR\&\fR\&, but only for attribute \fIAttribute\fR\&\&.
.RE

.LP
.nf

.B
expr(Expression) -> io_lib:chars()
.br
.fi
.br
.nf

.B
expr(Expression, Options) -> io_lib:chars()
.br
.fi
.br
.nf

.B
expr(Expression, Indent, Options) -> io_lib:chars()
.br
.fi
.br
.nf

.B
expr(Expression, Indent, Precedence, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Expression = \fBerl_parse:abstract_expr()\fR\&
.br
Indent = integer()
.br
Precedence = integer() >= 0
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Prints one expression\&. It is useful for implementing hooks (see section \fBKnown Limitations\fR\&)\&.
.RE

.LP
.nf

.B
exprs(Expressions) -> io_lib:chars()
.br
.fi
.br
.nf

.B
exprs(Expressions, Options) -> io_lib:chars()
.br
.fi
.br
.nf

.B
exprs(Expressions, Indent, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Expressions = [\fBerl_parse:abstract_expr()\fR\&]
.br
Indent = integer()
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Same as \fB\fIform/1,2\fR\&\fR\&, but only for the sequence of expressions in \fIExpressions\fR\&\&.
.RE

.LP
.nf

.B
form(Form) -> io_lib:chars()
.br
.fi
.br
.nf

.B
form(Form, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Form = \fBerl_parse:abstract_form()\fR\& | \fBerl_parse:form_info()\fR\&
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Pretty prints a \fIForm\fR\&, which is an abstract form of a type that is returned by \fB\fIerl_parse:parse_form/1\fR\&\fR\&\&.
.RE

.LP
.nf

.B
function(Function) -> io_lib:chars()
.br
.fi
.br
.nf

.B
function(Function, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Function = \fBerl_parse:abstract_form()\fR\&
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Same as \fB\fIform/1,2\fR\&\fR\&, but only for function \fIFunction\fR\&\&.
.RE

.LP
.nf

.B
guard(Guard) -> io_lib:chars()
.br
.fi
.br
.nf

.B
guard(Guard, Options) -> io_lib:chars()
.br
.fi
.br
.RS
.LP
Types:

.RS 3
Guard = [\fBerl_parse:abstract_expr()\fR\&]
.br
Options = \fBoptions()\fR\&
.br
.RE
.RE
.RS
.LP
Same as \fB\fIform/1,2\fR\&\fR\&, but only for the guard test \fIGuard\fR\&\&.
.RE

.SH "KNOWN LIMITATIONS"

.LP
It is not possible to have hook functions for unknown forms at other places than expressions\&.
.SH "SEE ALSO"

.LP
\fB\fIerl_eval(3erl)\fR\&\fR\&, \fB\fIerl_parse(3erl)\fR\&\fR\&, \fB\fIio(3erl)\fR\&\fR\&