Find out we are running under emacs?

[JanWielemaker]

Most emacs mode that create a process put something into the environment such that the process can act on this mode. Currently SW-Prolog checks for EMACS, INSIDE_EMACS and INFERIOR. It would be nice if ediprolog did that as well. Or do we have some other not-to-wild way to discover we are running under ediprolog? Testing the prompt is all I can think of right now ...

[triska]

Can this be handled analogously to SWI-Prolog/swipl-devel@044aabc ?

[JanWielemaker]

Hmmm. As a hack, possibly (but then we also have checking the prompt). In general I'd guess a dumb terminal is still ok to do basic paging, while it is not good enough for commandline editing. I'll probably implement some quick fix for now, but it would be nice if there was a more robust way to find out that we are running under ediprolog.

[triska]

One important point for the immediate ad hoc solution: The default prompt that ediprolog uses is:

?ediprolog- .

Please see:

ediprolog/ediprolog.el

Line 138 in 6f94bf2

(defvar ediprolog-prompt "?ediprolog- "

This is user-configurable, though I do not expect many changes in this area, also not for the immediate future.

[JanWielemaker]

However,

?- prompt(X,X).
%@ X = '|: '.

I think it makes the point clear that using the prompt is not a good way to find ediprolog (especially if it can be configured). For now, TERM does the job, but who know whether that should be reverted at some point because there are dumb terminals where you want (elementary) paging?

Most related emacs functionality such as M-x shell seem to do this using an environment variable. Unfortunately they all use their own ...

[triska]

ediprolog sets the prompt with '$set_prompt'/1:

ediprolog/ediprolog.el

Line 233 in 6f94bf2

'$set_prompt'('%s').\n" ediprolog-prompt)))

You can see the exact toplevel interaction in the buffer *ediprolog-history*. For example, in the case you posted:

?ediprolog-  prompt(X, X).
X = '|: '.

?ediprolog- 

[JanWielemaker]

Thanks. That explains something. Now changed the test to

running_under_emacs :-
    current_prolog_flag(toplevel_prompt, P),
    sub_atom(P, _, _, _, 'ediprolog'),
    !.

Note that '$set_promp'/1 is deprecated and new code should use the Prolog flag. As this is not a hard constant it is still a shaky way to find emacs/ediprolog.

As a side note, wouldn't it be a good idea to do something similar as for PDT where we have library(pdt_console) and add a library(ediprolog_console) where we can do whatever is needed to facilitate ediprolog?