Resolving dependencies...
cabal: Could not resolve dependencies:
next goal: once (user goal)
rejecting: once-0.2 (constraint from user target requires ==0.1.0.0)
trying: once-0.1.0.0
trying: base-4.9.0.0/installed-4.9... (dependency of once-0.1.0.0)
next goal: template-haskell (dependency of once-0.1.0.0)
rejecting: template-haskell-2.11.0.0/installed-2.1...,
template-haskell-2.11.0.0 (conflict: once => template-haskell==2.10.*)
rejecting: template-haskell-2.10.0.0 (conflict:
base==4.9.0.0/installed-4.9..., template-haskell => base==4.8.*)
rejecting: template-haskell-2.9.0.0, template-haskell-2.8.0.0,
template-haskell-2.7.0.0, template-haskell-2.6.0.0, template-haskell-2.5.0.0,
template-haskell-2.4.0.1, template-haskell-2.4.0.0, template-haskell-2.3.0.1,
template-haskell-2.3.0.0, template-haskell-2.2.0.0 (conflict: once =>
template-haskell==2.10.*)
Dependency tree exhaustively searched.