Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: Pugs (user goal)
rejecting: Pugs-6.2.13.20150815, Pugs-6.2.13.20130611, Pugs-6.2.13.20120717,
Pugs-6.2.13.20120203 (constraint from user target requires ==6.2.13.20111008)
trying: Pugs-6.2.13.20111008
trying: pugs-DrIFT-2.2.3.20150815 (dependency of Pugs-6.2.13.20111008)
next goal: mtl (dependency of Pugs-6.2.13.20111008)
rejecting: mtl-2.2.1, mtl-2.2.0.1, mtl-2.2, mtl-2.1.3.1, mtl-2.1.2, mtl-2.1.1,
mtl-2.1, mtl-2.0.1.1, mtl-2.0.1.0, mtl-2.0.0.0 (conflict: Pugs => mtl<2.0.0.0)
rejecting: mtl-1.1.1.1, mtl-1.1.1.0, mtl-1.1.0.2, mtl-1.1.0.1, mtl-1.1.0.0,
mtl-1.0 (conflict: pugs-DrIFT => mtl>=2.0.0.0)
Dependency tree exhaustively searched.