Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: yesod-platform (user goal)
rejecting: yesod-platform-1.2.13.3, yesod-platform-1.2.13.2,
yesod-platform-1.2.13.1, yesod-platform-1.2.13, yesod-platform-1.2.12.4,
yesod-platform-1.2.12.3, yesod-platform-1.2.12.2, yesod-platform-1.2.12.1
(constraint from user target requires ==1.2.12)
trying: yesod-platform-1.2.12
trying: base-4.9.0.0/installed-4.9... (dependency of yesod-platform-1.2.12)
next goal: yaml (dependency of yesod-platform-1.2.12)
rejecting: yaml-0.8.21.1, yaml-0.8.21, yaml-0.8.20, yaml-0.8.19.0,
yaml-0.8.18.7, yaml-0.8.18.6, yaml-0.8.18.5, yaml-0.8.18.4, yaml-0.8.18.3,
yaml-0.8.18.2, yaml-0.8.18.1, yaml-0.8.18, yaml-0.8.17.2, yaml-0.8.17.1,
yaml-0.8.17, yaml-0.8.16, yaml-0.8.15.3, yaml-0.8.15.2, yaml-0.8.15.1,
yaml-0.8.14, yaml-0.8.13, yaml-0.8.12, yaml-0.8.11, yaml-0.8.10.1,
yaml-0.8.10, yaml-0.8.9.4, yaml-0.8.9.3, yaml-0.8.9.2, yaml-0.8.9.1,
yaml-0.8.9, yaml-0.8.8.4 (conflict: yesod-platform => yaml==0.8.8.3)
rejecting: yaml-0.8.8.3 (conflict: base==4.9.0.0/installed-4.9..., yaml =>
base>=4 && <4.8)
rejecting: yaml-0.8.8.2, yaml-0.8.8.1, yaml-0.8.8, yaml-0.8.7.2, yaml-0.8.7.1,
yaml-0.8.7, yaml-0.8.6.2, yaml-0.8.6.1, yaml-0.8.6, yaml-0.8.5.4,
yaml-0.8.5.3, yaml-0.8.5.2, yaml-0.8.5.1, yaml-0.8.5, yaml-0.8.4.1,
yaml-0.8.4, yaml-0.8.3, yaml-0.8.2.4, yaml-0.8.2.3, yaml-0.8.2.2,
yaml-0.8.2.1, yaml-0.8.2, yaml-0.8.1.2, yaml-0.8.1.1, yaml-0.8.1,
yaml-0.8.0.2, yaml-0.8.0.1, yaml-0.8.0, yaml-0.7.0.4, yaml-0.7.0.3,
yaml-0.7.0.2, yaml-0.7.0.1, yaml-0.7.0, yaml-0.6.1, yaml-0.6.0, yaml-0.5.2,
yaml-0.5.1.2, yaml-0.5.1.1, yaml-0.5.1, yaml-0.5.0.1, yaml-0.5.0,
yaml-0.4.1.2, yaml-0.4.1.1, yaml-0.4.1, yaml-0.4.0, yaml-0.3.0, yaml-0.2.1,
yaml-0.2.0, yaml-0.0.4, yaml-0.0.3, yaml-0.0.2, yaml-0.0.1, yaml-0.0.0
(conflict: yesod-platform => yaml==0.8.8.3)
Dependency tree exhaustively searched.