I see your point, i.e., compiled, multi-file projects are not really meant
for the REPL-dominant world of org-mode babel. Babel's sweet-spot would be
the interpreted world, the very best probably a Lisp language. Still, the
ability to add code to a running REPL should be possible. As I mentioned,
SML is a sibling of Haskell and its babel implementation worked fine for me
as I worked through an SML course. So yes, this appears to be a Haskell
REPL issue. I'm just a beginner with Haskell, and all my intro texts start
you out using the ghci REPL interactively. But then they switch you over to
a text file compiled in the REPL with :l myfile.hs . . . no explanation as
to why you can't just continue with the REPL putting the program in
line-by-line. The fact that I can use the :set +m to include multiple lines
of code, but cannot do a type definition is rather bizarre, though. This is
a decision Haskell made with their REPL and babel really can't do much
about it, I suppose. The Haskell .lhs literate option is interesting. Yes,
I'd like to see your tangle option, please.

On Thu, Dec 10, 2020 at 4:28 AM Immanuel Litzroth <
immanuel.litzroth@gmail.com> wrote:

> I don't think org-babel is a good fit for compiled languages. If the
> idea is to just take 1 snippet,
> and "execute" that it means that to have a consistent whole you'd need
> to put all the modules of
> your program into that snippet (already impossible in Haskell, you can
> have only 1 module per file),
> compile that, run the resulting binary. Or org mode would have to have
> some idea of what needs to
> be retangled & rebuilt.
> I think that using org-babel for compiled, multifile languages will
> only work in very simple cases -- and
> even then.. -- but will lead to problems very soon.
> Immanuel
>
> On Thu, Dec 10, 2020 at 4:21 AM Lawrence Bottorff <borgauf@gmail.com>
> wrote:
> >
> > I'm looking into Haskell (latest ghci) again on org-mode. This
> >
> > #+begin_src haskell :results verbatim :exports both
> > :set +m
> > doubleSmallNumber x = if x > 100
> >   then x
> >   else x*2
> > #+end_src
> >
> > works, but still the :set +m is necessary for it to see the whole. But
> this
> >
> > #+begin_src haskell :results verbatim :exports both
> > :set +m
> > factorial :: Int -> Int
> > factorial 0 = 1
> > factorial n = n * factorial (n - 1)
> > #+end_src
> >
> > results in this on the REPL side:
> >
> > Prelude> :set +m
> > factorial :: Int -> Int
> > factorial 0 = 1
> > factorial n = n * factorial (n - 1)
> > "org-babel-haskell-eoe"
> > Prelude>
> > <interactive>:26:1-23: error:
> >     • No instance for (Show (Int -> Int)) arising from a use of ‘print’
> >         (maybe you haven't applied a function to enough arguments?)
> >     • In a stmt of an interactive GHCi command: print it
> > Prelude> Prelude> Prelude> "org-babel-haskell-eoe"
> >
> > which is the same behavior if I try to feed the program into the REPL
> one line at a time, i.e.,
> >
> > Prelude> factorial :: Int -> Int
> >
> > <interactive>:40:1-23: error:
> >     • No instance for (Show (Int -> Int)) arising from a use of ‘print’
> >         (maybe you haven't applied a function to enough arguments?)
> >     • In a stmt of an interactive GHCi command: print it
> >
> > So the :set +m trick (take multiple lines) doesn't help here. Obviously,
> Haskell is not ready to be used with Babel. Can it be fixed? BTW, this does
> work with the regular ghci REPL and haskell-mode. If it helps, Standard ML,
> which has very similar syntax (it was Haskell's parent), works fine.
> >
> > LB
>
>
>
> --
> -- Researching the dual problem of finding the function that has a
> given point as fixpoint.
>