Default to exec'ing ghci in sandbox if present? about ghcid

[ndmitchell]

The problem with cabal exec is that it's slow, and in older versions, buggy (if there is any compile error it bails out rather than opening ghci with a compile error). What is the difference between cabal exec and cabal repl? Having arguments be :loaded seems like a reasonable idea, and might have been enough in conjunction with cabal repl to make your third command work.

[istathar]

The problem with cabal exec is that it's slow

Well, that's mitigated by the fact that the whole point of ghcid would seem to be running the child GHCi process only once, so wrapping it in cabal exec isn't going to hurt. [Day to day I am running the above command via a shell script:

$ cat ~/.local/bin/build 
exec ghcid --command="cabal exec ghci $*"
$

thence build tests/ThoughtExperiment.hs, (because I keep trying to do cabal exec ghcid, which is wrong but seems reasonable)].

What is the difference between cabal exec and cabal repl?

As far as I can tell, cabal repl will only load a named section from the .cabal file (executable, test suite, or benchmark) and not just an arbitrary file — which does work with the pattern above

Having arguments be :loaded seems like a reasonable idea, and might have been enough in conjunction with cabal repl to make your third command work.

Quite possibly, but type checking ad-hoc scripts is where this is really shining for me for the moment, and lord knows having to enumerate each and every junk test program in your .cabal file just to repl it is tedious at best.

AfC

[ndmitchell]

One of the reasons I regularly stop/start my ghcid is to save my laptop battery, which I guess #26 is the real fix for. So I guess what we need is an algorithm to go from a directory with files in it, and optionally a list of files, to a command line and list of commands. Currently that algorithm is https://github.com/ndmitchell/ghcid/blob/master/src/Ghcid.hs#L51 and has no support for free command line arguments. It seems what you are suggesting is roughly:

• If you have a .cabal file in the directory, and no arguments, do cabal repl.
• If you have a .cabal file in the directory, and some arguments, do cabal exec ghci <arguments>.
• Otherwise, do ghci <arguments>

Does that seem about right?

One thing that seems not to work with that is that if I import Paths_shake into a module then cabal exec doesn't work, but cabal repl does. Any thoughts on how to avoid that?

[ndmitchell]

I've rewritten it, so now ghcid tests/Experiment.hs works, which will do a cabal exec ghci tests/Experiment.hs for you under the covers. Please let me know if there are still undesirable cases.