edif is a GNU APL native function that allows the use of external editors from within an APL session.

Usage:

edif 'function_name'
or
edif2 'function_name'

Both of these will open an editor, typically vi or emacs, containing the present definition of the specified function, or, if the function doesn't exist, a boilerplate function header consisting of the function name. After saving the edited definition and exiting the editor, the function will appear in the APL workspace. (In the case of a new function, the boilerplate name can be edited as necessary:

fubar

can be edited to

z←x fubar y

and the right thing will be fixed in APL. (Even existing functions can be modified this way.))

The two versions of the function differ in that the first version, edif, suspends the current APL session until the editor is closed, while the second version, edif2, opens the editor in a separate process, in a separate window, while the APL session remains active. This allows functions to be edited and tested concurrently without having to go into and out of the editor. edif2 also allows multiple editor windows to be open simultaneously on different functions.

Both versions have a dyadic form:

'editor' edif 'function_name'
or
'editor' edif2 'function_name'

where 'editor' is the editor to be invoked. For example:

'vi' edif 'fubar'

would open function fubar using the vi editor.

'emacs' edif2 'fu'
'emacs' edif2 'bar'

would open functions fu and bar in separate emacs windows.

edif will look for the environment variable EDIF and will use the string specified by that variable as the command line to invoke the chosen editor. For example:

export EDIF="nano"

will cause edif to default to using the nano editor. Similarly, the EDIF2 variable affects the default edif2 editor.

edif has been tested with emacs, vi, and nano; edif2 with emacs and gvim. The default editor for edif is vi; the default for edif2 is

"emacs --geometry=40x20 -background '#ffffcc' -font 'DejaVu Sans Mono-10'"

The dyadic forms remember the chosen editors and sets them as replacement defaults for the duration of the session.

edif may be included in the workspace with:

'libedif.so' ⎕fx 'edif'

and edif2 with:

'libedif2.so' ⎕fx 'edif2'

Of course, you can use any function names you like and, as long as you use different names, both versions can be used at the same time.

edif and edif2 can both be invoked with an option in what's usually used as the axis specifier. An option of [1] forces edif into lambda mode:

    edif2 [1] 'fu'

would open a boilerplate lambda function consisting of just the assignment ("fu←") and allowing the user to enter the body. (E,g., "{⍺ + ⍵}") (It's the user's responsibility to ensure that the body meets the requirements of a lambda.) Subsequent openings of the same lambda automatically go into lambda mode even if the option is omitted.

edif2 [2] ''

returns the current GNU APL version while

edif2 [3] ''

returns the git commit log signature of the most recent edif build.

So far as I can tell, edif doesn't interfere with Elias Mårtenson's emacs APL mode, but I haven't thoroughly tested that.

By the way, "edif" is short for "editor interface."

Implimentation note:

edif and edif2 work by storing an editable version of the specified function in:

/var/run/user/<uid>/<pid>/<name>.apl

where is the user's userid, is the process id of the APL session, and is the function name. This allows multiple users each to have multiple simultaneous APL sessions with workspaces with identical names. No locking is done by edif and I've no idea if APL itself has any protection against a writable workspace being open in multiple simultaneous sessions, but it opens up the possibility that you can hose the workspace. So while, as far as edif is concerned you can have multiple simultaneous sessions aimed at the same lib0 workspace, you probably shouldn't do it.

Also, I've no idea if Windows or any Linux distribution other than Fedora has a /var directory, so using this directory may be non-portable.