[Haskell-beginners] Getting started with repa on MacOS

[Andres Löh]

Hi.

> Unfortunately I didn't get very far, because I am stuck at installing repa:
>
>        cabal install repa
>        Resolving dependencies...
>        cabal: cannot configure repa-2.2.0.1. It requires base ==4.4.*
>        For the dependency on base ==4.4.* there are these packages: base-4.4.0.0.
>        However none of them are available.
>        base-4.4.0.0 was excluded because of the top level dependency base -any

There are two issues here:

(1) The latest version of repa doesn't work with ghc-7.0.3 or
ghc-7.0.4. These provide base-4.3, and base is hardwired in GHC and
cannot be upgraded. The easiest way for you to get around this is to
explicitly say "cabal install repa-2.1.1.5".

(2) Your version of cabal-install provides bad feedback (instead of
base -any it should really say that it has to be the version of base
that comes with your GHC) and fails to detect that it in fact could
just install repa-2.1.1.5. The current development version of
cabal-install fixes both problems. However, as long as the fix
suggested in (1) works for you, there's no immediate need to upgrade.

Cheers,
  Andres