# 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.

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`.

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()) -> context()`

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 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.

### AUTHORS

Richard Carlsson - support@erlang.ericsson.se

syntax_tools 1.5.2
Copyright © 1991-2007 Ericsson AB