Stack doesn't install correct version of Haskell base library

Question

I am fairly new to Haskell. I am trying to build a project downloaded from GitHub using stack. When I try to run stack solver, I get this output:

cabal: Could not resolve dependencies:
trying: deeplearning-hs-0.1.0.2 (user goal)
next goal: base (dependency of deeplearning-hs-0.1.0.2)
rejecting: base-4.8.1.0/installed-075... (conflict: deeplearning-hs =>
base>=4.6 && <4.7)
rejecting: base-4.8.1.0 (global constraint requires installed instance)
rejecting: base-4.8.0.0, 4.7.0.2, 4.7.0.1, 4.7.0.0, 4.6.0.1, 4.6.0.0, 4.5.1.0,
4.5.0.0, 4.4.1.0, 4.4.0.0, 4.3.1.0, 4.3.0.0, 4.2.0.2, 4.2.0.1, 4.2.0.0,
4.1.0.0, 4.0.0.0, 3.0.3.2, 3.0.3.1 (global constraint requires ==4.8.1.0)
Dependency tree exhaustively searched.

The issue seems to be this "global constraint" but I'm not sure where that's coming from. I have looked through my global .cabal files and they are pretty generic--they don't seem to specify the versions of anything.

phadej · Accepted Answer · 2015-12-27 08:23:38Z

2

base is a library bundled with GHC (the compiler). For each GHC version, there is one base version.

To install deeplearning-hs, seems you need to satisfy base == 4.6.* constraint, i.e. have GHC version 7.6. Unfortunately you cannot install GHC older then 7.8 with stack AFAIK.

You can play with it locally if you change base >=4.6 && <4.7 bounds to base >= 4.6 && <4.8, i.e. allow base coming with GHC 7.8 for example. Note, you shouldn't remove dependencies, you should try to relax the constraints (i.e. version bounds). I tried locally, and the package seems to compile with GHC 7.8. It doesn't compile with GHC 7.10 as Foldable-Traversal-Proposal affects this package.

IMHO best way is to contact the maintainer and ask for upgrade, or even better submit a pull request, as source seems to be on GitHub (which I did).

P.S. I relaxed the bounds on Hackage, so you can install it with GHC 7.8 without worries now.

edited Dec 27, 2015 at 8:23

answered Dec 25, 2015 at 15:28

phadej

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2 Comments

Sibi Over a year ago

Probably he can try editing the cabal file and see if things work with the new GHC. :)

ethanabrooks Over a year ago

I see. I didn't know about the GHC >= 7.8 constraint for stack. I did try editing the cabal file by commenting out the requirements for base >=4.6 && <4.7, and ran into the following: Could not find module ‘Data.List’ It is a member of the hidden package ‘base-4.8.1.0’. and same for ‘Prelude.’ Perhaps it is best to work on this one without Stack, which I guess means downloading the older version of GHC?

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