Resolving dependencies...
cabal: Could not resolve dependencies:
[__0] trying: devtools-0.0.2 (user goal)
[__1] trying: source-constraints-0.0.1 (dependency of devtools)
[__2] next goal: base (dependency of devtools)
[__2] rejecting: base-4.12.0.0/installed-4.12.0.0 (conflict:
source-constraints => base>=4.13 && <4.14)
[__2] skipping: base-4.14.0.0 (has the same characteristics that caused the
previous version to fail: excluded by constraint '>=4.13 && <4.14' from
'source-constraints')
[__2] rejecting: base-4.13.0.0, base-4.12.0.0, base-4.11.1.0, base-4.11.0.0,
base-4.10.1.0, base-4.10.0.0, base-4.9.1.0, base-4.9.0.0, base-4.8.2.0,
base-4.8.1.0, base-4.8.0.0, base-4.7.0.2, base-4.7.0.1, base-4.7.0.0,
base-4.6.0.1, base-4.6.0.0, base-4.5.1.0, base-4.5.0.0, base-4.4.1.0,
base-4.4.0.0, base-4.3.1.0, base-4.3.0.0, base-4.2.0.2, base-4.2.0.1,
base-4.2.0.0, base-4.1.0.0, base-4.0.0.0, base-3.0.3.2, base-3.0.3.1
(constraint from non-upgradeable package requires installed instance)
[__2] fail (backjumping, conflict set: base, devtools, source-constraints)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: base, devtools, source-constraints