Re: [PATCH] ob-haskell: Line Continuations Mangle Block Output

[Kyle Meyer <kyle@kyleam.com>]

Nick Daly writes:

> After a bit of tinkering, I realized there are two things going on
> here, only one of which I fully understand:
>
> 1. My core functional issue is that =comint-prompt-regexp= isn't set
>    up to handle the "Prelude| " entries or the repeated prompts.  The
>    other patches I submitted were unnecessary.
>
> 2. The =comint-prompt-regexp= gets default values from somewhere I
>    don't understand and can't find with a quick source grep.

Here's what I can gather.  inf-haskell used to set comint-prompt-regexp
in the body of inferior-haskell-mode.  Here's an example from 11d6abf
(2017-08-24):

  (setq-local comint-prompt-regexp
                ;; Why the backslash in [\\._[:alnum:]]?
                "^\\*?[[:upper:]][\\._[:alnum:]]*\\(?: \\*?[[:upper:]][\\._[:alnum:]]*\\)*\\( λ\\)?> \\|^λ?> $")

In ca94d81 (revamped inf-haskell, 2017-08-26), which was included in the
v17.1 release, haskell-prompt-regexp was introduced and the line above
is now

  (setq-local comint-prompt-regexp haskell-prompt-regexp)

> In ob-haskell, we set =comint-prompt-regexp= to the (undefined)
> haskell-prompt plus "or optional-lambda":

With a haskell-mode after the commit I point to above, it shouldn't be
undefined at the time we set comint-prompt-regexp because
org-babel-interpret-haskell loads inf-haskell before that.

However, I'm confused why Org's b46787743 (Fix ob-haskell.el to work
with custom ghci prompts, 2017-12-02) added the λ bit (author of that
patch cc'd).  As far as I can tell, that is a part of
inferior-haskell-mode's default comint-prompt-regexp and has been since
28997b2 (Add support for popular "λ> " prompt to inf-haskell,
2013-07-04).

You've sent an updated patch in a follow-up message, so I'll continue
there...