## 4.4 Editor Interface

SWI-Prolog offers an extensible interface which allows the user to edit objects of the program: predicates, modules, files, etc. The editor interface is implemented by edit/1 and consists of three parts: locating, selecting and starting the editor. Any of these parts may be customized. See section 4.4.1.

The built-in edit specifications for edit/1 (see prolog_edit:locate/3) are described in the table below:

Fully specified objects
<Module>:<Name>/<Arity> | Refers to a predicate
module(<Module>) | Refers to a module
file(<Path>) | Refers to a file
source_file(<Path>) | Refers to a loaded source file
Ambiguous specifications
<Name>/<Arity> | Refers to this predicate in any module
<Name> | Refers to (1) the named predicate in any module with any arity, (2) a (source) file, or (3) a module.

edit(+Specification)
  First, exploit prolog_edit:locate/3 to translate Specification into a list of Locations. If there is more than one‘hit', the user is asked to select from the locations found. Finally, prolog_edit:edit_source/1 is used to invoke the user's preferred editor. Typically, edit/1 can be handed the name of a predicate, module, basename of a file, XPCE class, XPCE method, etc.
edit
  Edit the‘default' file using edit/1. The default file is either the first `.pl` file from the commandline (the associated file, see the Prolog flag associated_file or the first script file specified using the -s or -l command line option. When using the Windows shell while SWI-Prolog is associated with the `.pl` extension this is the file loaded by double-clicking a `.pl` file. See also section 2.11.1.1.

### 4.4.1 Customizing the editor interface

The predicates described in this section are hooks that can be defined to disambiguate specifications given to edit/1, find the related source, and open an editor at the given source location.

prolog_edit:locate(+Spec, -FullSpec, -Location)
  Where Spec is the specification provided through edit/1. This multifile predicate is used to enumerate locations where an object satisfying the given Spec can be found. FullSpec is unified with the complete specification for the object. This distinction is used to allow for ambiguous specifications. For example, if Spec is an atom, which appears as the basename of a loaded file and as the name of a predicate, FullSpec will be bound to `file(Path)` or Name/Arity.

  Location is a list of attributes of the location. Normally, this list will contain the term `file(File)` and, if available, the term `line(Line)`.

prolog_edit:locate(+Spec, -Location)
  Same as prolog_edit:locate/3, but only deals with fully specified objects.
prolog_edit:edit_source(+Location)
  Start editor on Location. See prolog_edit:locate/3 for the format of a location term. This multifile predicate is normally not defined. If it succeeds, edit/1 assumes the editor is started.

  If it fails, edit/1 uses its internal defaults, which are defined by the Prolog flag editor and/or the environment variable `EDITOR`. The following rules apply. If the Prolog flag editor is of the format `$`<name>, the editor is determined by the environment variable <name>. Else, if this flag is `pce_emacs` or `built_in` and XPCE is loaded or can be loaded, the built-in Emacs clone is used. Else, if the environment `EDITOR` is set, this editor is used. Finally, vi is used as default on Unix systems and notepad on Windows.

  See the default user preferences file `customize/init.pl` for examples.

prolog_edit:edit_command(+Editor, -Command)
  Determines how Editor is to be invoked using shell/1. Editor is the determined editor (see prolog_edit:edit_source/1), without the full path specification, and without a possible (`.exe`) extension. Command is an atom describing the command. The following %-sequences are replaced in Command before the result is handed to shell/1:

  %e | Replaced by the (OS) command name of the editor
  %f | Replaced by the (OS) full path name of the file
  %d | Replaced by the line number

  If the editor can deal with starting at a specified line, two clauses should be provided. The first pattern invokes the editor with a line number, while the second is used if the line number is unknown.

  The default contains definitions for vi, emacs, emacsclient, vim, notepad^* and wordpad^*. Starred editors do not provide starting at a given line number.

  Please contribute your specifications to bugs@swi-prolog.org.

prolog_edit:load
  Normally an undefined multifile predicate. This predicate may be defined to provide loading hooks for user extensions to the edit module. For example, XPCE provides the code below to load `library(swi_edit)`, containing definitions to locate classes and methods as well as to bind this package to the PceEmacs built-in editor.

      :- multifile prolog_edit:load/0.

      prolog_edit:load :-
              ensure_loaded(library(swi_edit)).