SWI-Prolog binding to BSD libedit
Jan Wielemaker
VU University Amsterdam
CWI, Amsterdam
The Netherlands
E-mail: J.Wielemaker@vu.nl
Abstract
This package enables editing commands in the Prolog toplevel using the BSD libedit library.

# Table of Contents

## 1 library(editline): BSD libedit based command line editing

This library wraps the BSD libedit command line editor. The binding provides a high level API to enable command line editing on the Prolog user streams and low level predicates to apply the library on other streams and program the library.

[det]el_wrap
  Enable using editline on the standard user streams if `user_input` is connected to a terminal. This is the high level predicate used for most purposes. The remainder of the library interface deals with low level predicates that allows for applying and programming libedit in non-standard situations.

  The library is registered with ProgName set to `swipl` (see el_wrap/4).

[det]el_wrap(+ProgName:atom, +In:stream, +Out:stream, +Error:stream)
  Enable editline on the stream-triple <In,Out,Error>. From this moment on In is a handle to the command line editor.

  ProgName | is the name of the invoking program, used when reading the `editrc(5)` file to determine which settings to use.

[nondet,multifile]el_setup(+In:stream)
  This hooks is called as `forall(el_setup(Input), true)` after the input stream has been wrapped, the default Prolog commands have been added and the default user setup file has been sourced using el_source/2. It can be used to define and bind additional commands.
[semidet]el_wrapped(+In:stream)
  True if In is a stream wrapped by el_wrap/3.
[det]el_unwrap(+In:stream)
  Remove the libedit wrapper for In and the related output and error streams.
  bug
    The wrapper creates `FILE*` handles that cannot be closed and thus wrapping and unwrapping implies a (modest) memory leak.
[det]el_source(+In:stream, +File)
  Initialise editline by reading the contents of File. If File is unbound try `$HOME/.editrc`
[det]el_bind(+In:stream, +Args)
  Invoke the libedit `bind` command with the given arguments. The example below lists the current key bindings.

      ?- el_bind(user_input, ['-a']).

  The predicate el_bind/2 is typically used to bind commands defined using el_addfn/4. Note that the C proxy function has only the last character of the command as context to find the Prolog binding. This implies we cannot both bind e.g., "`^`[?" *and "?" to a Prolog function.

  See also
    `editrc(5)` for more information.
[det]el_addfn(+Input:stream, +Command, +Help, :Goal)
  Add a new command to the command line editor associated with Input. Command is the name of the command, Help is the help string printed with e.g. `bind -a` (see el_bind/2) and Goal is called of the associated key-binding is activated. Goal is called as

      call(:Goal, +Input, +Char, -Continue)

  where Input is the input stream providing access to the editor, Char the activating character and Continue must be instantated with one of the known continuation codes as defined by libedit: `norm`, `newline`, `eof`, `arghack`, `refresh`, `refresh_beep`, `cursor`, `redisplay`, `error` or `fatal`. In addition, the following Continue code is provided.

  electric(Move, TimeOut, Continue)
    Show electric caret at Move positions to the left of the normal cursor positions for the given TimeOut. Continue as defined by the Continue value.

  The registered Goal typically used el_line/2 to fetch the input line and el_cursor/2, el_insertstr/2 and/or el_deletestr/2 to manipulate the input line.

  Normally el_bind/2 is used to associate the defined command with a keyboard sequence.

  See also
    `el_set(3)` `EL_ADDFN` for details.
[det]el_line(+Input:stream, -Line)
  Fetch the currently buffered input line. Line is a term `line(Before, After)`, where Before is a string holding the text before the cursor and After is a string holding the text after the cursor.
[det]el_cursor(+Input:stream, +Move:integer)
  Move the cursor Move character forwards (positive) or backwards (negative).
[det]el_insertstr(+Input:stream, +Text)
  Insert Text at the cursor.
[det]el_deletestr(+Input:stream, +Count)
  Delete Count characters before the cursor.
[det]el_history(+In:stream, ?Action)
  Perform a generic action on the history. This provides an incomplete interface to `history()` from libedit. Supported actions are:
  clear
    Clear the history.
  setsize(+Integer)
    Set size of history to size elements.
  setunique(+Boolean)
    Set flag that adjacent identical event strings should not be entered into the history.
[det]el_history_events(+In:stream, -Events:list(pair))
  Unify Events with a list of pairs of the form `Num-String`, where Num is the event number and String is the associated string without terminating newline.
[det]el_add_history(+In:stream, +Line:text)
  Add a line to the command line history.
[det]el_read_history(+In:stream, +File:file)
  Read the history saved using el_write_history/2.

  File | is a file specification for absolute_file_name/3.

[det]el_write_history(+In:stream, +File:file)
  Save editline history to File. The history may be reloaded using el_read_history/2.

  File | is a file specification for absolute_file_name/3.

# Index

?
el_add_history/2
el_addfn/4
el_bind/2
el_cursor/2
el_deletestr/2
el_history/2
el_history_events/2
el_insertstr/2
el_line/2
el_read_history/2
el_setup/1
el_source/2
el_unwrap/1
el_wrap/0
el_wrap/4
el_wrapped/1
el_write_history/2