# erl_pp

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Module

erl_pp

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Module Summary

The Erlang pretty printer.

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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.

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Data Types

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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.

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option() =
{hook, hook_function()} |
{encoding, latin1 | unicode | utf8} |
{quote_singleton_atom_types, boolean()} |
{linewidth, integer() >= 1} |
{indent, integer() >= 1}

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

The option linewidth controls the maximum line width for formatted lines (defaults to 72 characters).

The option indent controls the indention for formatted lines (defaults to 4 spaces).

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

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Exports

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attribute(Attribute) -> io_lib:chars()

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

### Types

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

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

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expr(Expression) -> io_lib:chars()

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

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

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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).

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exprs(Expressions) -> io_lib:chars()

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

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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.

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form(Form) -> io_lib:chars()

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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.

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function(Function) -> io_lib:chars()

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

### Types

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

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

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guard(Guard) -> io_lib:chars()

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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.

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Known Limitations

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

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See Also

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