I'm trying to get Cabal to install the haskell-src-meta package, and I'm having difficulty with the template-haskell dependency. The dependencies for haskell-src-meta include both
template-haskell >=2.7 && <2.9,
template-haskell >=2.4 && <2.7,
It so happens that template-haskell versions 2.7 and later will not install on my system, but template-haskell 2.5.0.0 will install.
When I'm asking Cabal to install haskell-src-meta, how do I tell it to use template-haskell == 2.5.0.0?
Here is the full information for cabal info haskell-src-meta on my system:
* haskell-src-meta (library)
Synopsis: Parse source to template-haskell abstract syntax.
Latest version available: 0.5.1
Latest version installed: [ Not installed ]
Homepage: [ Not specified ]
Bug reports: https://github.com/benmachine/haskell-src-meta/issues
Description: The translation from haskell-src-exts abstract syntax to
template-haskell abstract syntax isn't 100% complete yet.
Category: Language
License: BSD3
Author: Matt Morrow
Maintainer: Ben Millwood <haskell@benmachine.co.uk>
Source repo: git://github.com/benmachine/haskell-src-meta.git
Flags: new-th
Dependencies: base >=4.2 && <4.6, haskell-src-exts >=1.8 && <1.12,
pretty >=1.0 && <1.2, syb >=0.1 && <0.4, th-lift ==0.5.*,
template-haskell >=2.7 && <2.9,
template-haskell >=2.4 && <2.7, uniplate >=1.3 && <1.7
Cached: No
Modules:
Language.Haskell.Meta
Language.Haskell.Meta.Parse
Language.Haskell.Meta.Parse.Careful
Language.Haskell.Meta.Syntax.Translate
Language.Haskell.Meta.Utils
Language.Haskell.TH.Instances.Lift
cabal install --constraint="template-haskell == 2.5.0.0" haskell-src-meta
来源：https://stackoverflow.com/questions/9657334/how-can-i-tell-cabal-which-dependency-to-use