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# erl_prettypr

### MODULE

erl_prettypr

### MODULE SUMMARY

Pretty printing of abstract Erlang syntax trees.

### DESCRIPTION

Pretty printing of abstract Erlang syntax trees.

This module is a front end to the pretty-printing library module prettypr, for text formatting of abstract syntax trees defined by the module erl_syntax.

### DATA TYPES

context()

  A representation of the current context of the pretty-printer. Can be accessed in hook functions.

hook() = (syntaxTree(), context(), Continuation) -> document()
  - Continuation = (syntaxTree(), context()) -> document()

  A call-back function for user-controlled formatting. See format/2.

### EXPORTS

best(Tree::syntaxTree()) -> empty | document()

Equivalent to best(Tree, []).

best(Tree::syntaxTree(), Options::[term()]) -> empty | document()

Creates a fixed "best" abstract layout for a syntax tree. This is similar to the layout/2 function, except that here, the final layout has been selected with respect to the given options. The atom empty is returned if no such layout could be produced. For information on the options, see the format/2 function.

See also: best/1, format/2, layout/2, prettypr:best/3.

format(Tree::syntaxTree()) -> string()

Equivalent to format(Tree, []).

format(Tree::syntaxTree(), Options::[term()]) -> string()

Types:

syntaxTree() (see module erl_syntax)

Prettyprint-formats an abstract Erlang syntax tree as text. For example, if you have a .beam file that has been compiled with debug_info, the following should print the source code for the module (as it looks in the debug info representation):

         {ok,{_,[{abstract_code,{_,AC}}]}} =
                 beam_lib:chunks("myfile.beam",[abstract_code]),
         io:put_chars(erl_prettypr:format(erl_syntax:form_list(AC)))

Available options:

{hook, none | hook()}

  Unless the value is none, the given function is called for each node whose list of annotations is not empty; see below for details. The default value is none.

{paper, integer()}

  Specifies the preferred maximum number of characters on any line, including indentation. The default value is 80.

{ribbon, integer()}

  Specifies the preferred maximum number of characters on any line, not counting indentation. The default value is 65.

{user, term()}

  User-specific data for use in hook functions. The default value is undefined.

{encoding, epp:source_encoding()}

  Specifies the encoding of the generated file.

A hook function (cf. the hook() type) is passed the current syntax tree node, the context, and a continuation. The context can be examined and manipulated by functions such as get_ctxt_user/1 and set_ctxt_user/2. The hook must return a "document" data structure (see layout/2 and best/2); this may be constructed in part or in whole by applying the continuation function. For example, the following is a trivial hook:

          fun (Node, Ctxt, Cont) -> Cont(Node, Ctxt) end

which yields the same result as if no hook was given. The following, however:

          fun (Node, Ctxt, Cont) ->
              Doc = Cont(Node, Ctxt),
              prettypr:beside(prettypr:text("<b>"),
                              prettypr:beside(Doc,
                                              prettypr:text("</b>")))
          end

will place the text of any annotated node (regardless of the annotation data) between HTML "boldface begin" and "boldface end" tags.

See also: erl_syntax, best/2, format/1, get_ctxt_user/1, layout/2, set_ctxt_user/2.

get_ctxt_hook(Ctxt::context()) -> hook()

Returns the hook function field of the prettyprinter context.

See also: set_ctxt_hook/2.

get_ctxt_linewidth(Ctxt::context()) -> integer()

Returns the line widh field of the prettyprinter context.

See also: set_ctxt_linewidth/2.

get_ctxt_paperwidth(Ctxt::context()) -> integer()

Returns the paper widh field of the prettyprinter context.

See also: set_ctxt_paperwidth/2.

get_ctxt_precedence(Ctxt::context()) -> integer()

Returns the operator precedence field of the prettyprinter context.

See also: set_ctxt_precedence/2.

get_ctxt_user(Ctxt::context()) -> term()

Returns the user data field of the prettyprinter context.

See also: set_ctxt_user/2.

layout(Tree::syntaxTree()) -> document()

Equivalent to layout(Tree, []).

layout(Tree::syntaxTree(), Options::[term()]) -> document()

Types:

document() (see module prettypr)

Creates an abstract document layout for a syntax tree. The result represents a set of possible layouts (cf. module prettypr). For information on the options, see format/2; note, however, that the paper and ribbon options are ignored by this function.

This function provides a low-level interface to the pretty printer, returning a flexible representation of possible layouts, independent of the paper width eventually to be used for formatting. This can be included as part of another document and/or further processed directly by the functions in the prettypr module, or used in a hook function (see format/2 for details).

See also: prettypr, format/2, layout/1.

set_ctxt_hook(Ctxt::context(), Hook::hook()) -> context()

Updates the hook function field of the prettyprinter context.

See also: get_ctxt_hook/1.

set_ctxt_linewidth(Ctxt::context(), W::integer()) -> context()

Updates the line widh field of the prettyprinter context.

Note: changing this value (and passing the resulting context to a continuation function) does not affect the normal formatting, but may affect user-defined behaviour in hook functions.

See also: get_ctxt_linewidth/1.

set_ctxt_paperwidth(Ctxt::context(), W::integer()) -> context()

Updates the paper widh field of the prettyprinter context.

Note: changing this value (and passing the resulting context to a continuation function) does not affect the normal formatting, but may affect user-defined behaviour in hook functions.

See also: get_ctxt_paperwidth/1.

set_ctxt_precedence(Ctxt::context(), Prec::integer()) -> context()

Updates the operator precedence field of the prettyprinter context. See the erl_parse(3) module for operator precedences.

See also: erl_parse(3), get_ctxt_precedence/1.

set_ctxt_user(Ctxt::context(), X::term()) -> context()

Updates the user data field of the prettyprinter context.

See also: get_ctxt_user/1.

Richard Carlsson carlsson.richard@gmail.com