Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: concurrent-output (user goal)
rejecting: concurrent-output-1.7.7, concurrent-output-1.7.6,
concurrent-output-1.7.5, concurrent-output-1.7.4, concurrent-output-1.7.3
(constraint from user target requires ==1.7.2)
trying: concurrent-output-1.7.2
trying: base-4.9.0.0/installed-4.9... (dependency of concurrent-output-1.7.2)
trying: mtl-2.2.1 (dependency of exceptions-0.8.3)
trying: transformers-compat-0.5.1.4 (dependency of exceptions-0.8.3)
next goal: transformers (dependency of concurrent-output-1.7.2)
rejecting: transformers-0.5.2.0/installed-0.5..., transformers-0.5.2.0,
transformers-0.5.1.0, transformers-0.5.0.1, transformers-0.5.0.0 (conflict:
concurrent-output => transformers(>=0.3.0 && <0.5.0))
rejecting: transformers-0.4.3.0, transformers-0.4.2.0 (conflict:
base==4.9.0.0/installed-4.9..., transformers => base>=2 && <4.9)
rejecting: transformers-0.4.1.0 (conflict: base==4.9.0.0/installed-4.9...,
transformers => base>=2 && <4.8 || >=1.0 && <2)
rejecting: transformers-0.3.0.0 (conflict: mtl => transformers>=0.4 && <0.6)
rejecting: transformers-0.2.2.1, transformers-0.2.1.0, transformers-0.2.0.0,
transformers-0.1.4.0, transformers-0.1.3.0, transformers-0.1.1.0,
transformers-0.1.0.1, transformers-0.0.1.0, transformers-0.0.0.0,
transformers-0.5.0.2 (conflict: concurrent-output => transformers(>=0.3.0 &&
<0.5.0))
rejecting: transformers-0.4.0.0 (conflict: transformers-compat =>
transformers>=0.3 && <0.4 || >=0.2 && <0.3 || >=0.4.1 && <0.6)
rejecting: transformers-0.2.2.0, transformers-0.1.0.0 (conflict:
concurrent-output => transformers(>=0.3.0 && <0.5.0))
Dependency tree exhaustively searched.