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.TH erl_pp 3 "stdlib 1.15.3" "Ericsson AB" "ERLANG MODULE DEFINITION"
.SH MODULE
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 EXPORTS
.LP
.B
form(Form) -> DeepCharList
.br
.B
form(Form, HookFunction) -> DeepCharList
.br
.RS
.TP
Types
Form = term()
.br
HookFunction = see separate description below\&.
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
Pretty prints a \fIForm\fR which is an abstract form of a type which is returned by \fIerl_parse:parse_form\fR\&.
.RE
.LP
.B
attribute(Attribute) -> DeepCharList
.br
.B
attribute(Attribute, HookFunction) -> DeepCharList
.br
.RS
.TP
Types
Attribute = term()
.br
HookFunction = see separate description below\&.
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
The same as \fIform\fR, but only for the attribute \fIAttribute\fR\&.
.RE
.LP
.B
function(Function) -> DeepCharList
.br
.B
function(Function, HookFunction) -> DeepCharList
.br
.RS
.TP
Types
Function = term()
.br
HookFunction = see separate description below\&.
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
The same as \fIform\fR, but only for the function \fIFunction\fR\&.
.RE
.LP
.B
guard(Guard) -> DeepCharList
.br
.B
guard(Guard, HookFunction) -> DeepCharList
.br
.RS
.TP
Types
Form = term()
.br
HookFunction = see separate description below\&.
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
The same as \fIform\fR, but only for the guard test \fIGuard\fR\&.
.RE
.LP
.B
exprs(Expressions) -> DeepCharList
.br
.B
exprs(Expressions, HookFunction) -> DeepCharList
.br
.B
exprs(Expressions, Indent, HookFunction) -> DeepCharList
.br
.RS
.TP
Types
Expressions = term()
.br
HookFunction = see separate description below\&.
.br
Indent = integer()
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
The same as \fIform\fR, but only for the sequence of expressions in \fIExpressions\fR\&.
.RE
.LP
.B
expr(Expression) -> DeepCharList
.br
.B
expr(Expression, HookFunction) -> DeepCharList
.br
.B
expr(Expression, Indent, HookFunction) -> DeepCharList
.br
.B
expr(Expression, Indent, Precedence, HookFunction) ->-> DeepCharList
.br
.RS
.TP
Types
Expression = term()
.br
HookFunction = see separate description below\&.
.br
Indent = integer()
.br
Precedence =
.br
DeepCharList = [char()|DeepCharList]
.br
.RE
.RS
.LP
This function prints one expression\&. It is useful for implementing hooks (see below)\&.
.RE
.SH UNKNOWN EXPRESSION HOOKS
.LP
The optional argument \fIHookFunction\fR, shown in the functions described above, defines a function which is called when an unknown form occurs where there should be a valid expression\&. It can have the following formats:
.RS 2
.TP 4
.B
\fIFunction\fR:
The hook function is called by:
.RS 4
.LP
.nf
Function(Expr,
CurrentIndentation,
CurrentPrecedence,
HookFunction)
.fi
.RE
.TP 4
.B
\fInone\fR:
There is no hook function
.RE
.LP
The called hook function should return a (possibly deep) list of characters\&. \fIexpr/4\fR is useful in a hook\&.
.LP
If \fICurrentIndentation\fR is negative, there will be no line breaks and only a space is used as a separator\&.
.SH BUGS
.LP
It should be possible to have hook functions for unknown forms at places other than expressions\&.
.SH SEE ALSO
.LP
io(3), erl_parse(3), erl_eval(3)
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