[Haskell-beginners] cabal and dependencies

[Andres Loeh]

Hi again.

> I had another issue with optional syntax highlighting support in gitit.
> The gitit web site says that if it available in pandoc then it is
> available in gitit too.
>
> Then the recommendation is:
> "To install gitit with highlighting support, first ensure that pandoc
> is compiled with highlighting support, then install gitit as above:
>
> cabal install pandoc -fhighlighting --reinstall
> cabal install gitit"
>
> If I do this it doesn't work because when installing gitit pandoc will
> be rebuilt again.
>
> I did: cabal install git pandoc -fhighlighting --reinstall
>
> which helped.
>
> I guess this fits also in the explanations you gave me.

Yes, it's somewhat similar, and you did the right thing. If you
request pandoc in isolation, it will be built against the versions of
its dependencies you already have installed, or, if you don't, against
the latest versions of these dependencies.

However, gitit introduces additional constraints, and the version of
pandoc you get when you ask for it individually currently doesn't meet
these constraints. By putting them both as targets on a single command
line, you get cabal to make a consistent install plan for both
packages.

Cheers,
  Andres