ob-haskell and changing executables?

[Laurence von Bottorff <borgauf@gmail.com>]

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I'm on Debian 12 and I just started using Haskell's ghcup tools, leaving
the stack tools behind, as advised these days. ghcup puts executables for
Haskell such as ghc, ghci (REPL), cabal, etc. in its ~/.ghcup/bin
directory. Next, to stop using the stack tools that have executables in
/usr/bin/ you must change your PATH to go to ~/.ghcup/bin first. But when I
try a Babel code block, ob-haskell seems to have the /usr/bin versions
hardwired somewhere and calls up the old ghci REPL. Searching through Emacs
Customize Haskell was confusing and my init only had one relevant entry
anyway, which didn't help when I changed it.

In the /usr/bin directory the Haskell execs are linked to just one specific
version. In my case /usr/bin contained symbolic links ghc -> ghc-9.0.2 and
ghci -> ghci-9.0.2. This is not great, since Haskell in the wild is
project-based, i.e., differing versions of the ghc compiler can be used in
different projects, as well as wildly diverging libraries and packages per
project. Obviously Babel can't easily take advantage of this, but Haskell
does allow "system-wide" library installs.

My solution was to simply delete the symlinks in /usr/bin and create new
ones to the ghcup tools, e.g., ghc -> ~/.ghcup/bin/ghc etc. So now it works
properly and calls up the new ghcup ghci when I do a Haskell Babel block,
but this is a kludge. No elisp master, I can't find where this /usr/bin
address is hardwired. If you've gotten this far you probably know more
about the Haskell Babel situation than you ever wanted to, but maybe you
can sniff out where this hardwire is happening.

-- 
⨽
Lawrence Bottorff
Grand Marais, MN, USA
borgauf@gmail.com

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