Resolving dependencies...
Downloading rfc3339-1.0.2...
Configuring rfc3339-1.0.2...
Building rfc3339-1.0.2...
Preprocessing library rfc3339-1.0.2...
[1 of 1] Compiling Data.Time.RFC3339 ( Data/Time/RFC3339.hs, dist/build/Data/Time/RFC3339.o )

Data/Time/RFC3339.hs:43:10:
    Illegal instance declaration for `RFC3339 String'
      (All instance types must be of the form (T a1 ... an)
       where a1 ... an are *distinct type variables*,
       and each type variable appears at most once in the instance head.
       Use -XFlexibleInstances if you want to disable this.)
    In the instance declaration for `RFC3339 String'
Failed to install rfc3339-1.0.2
cabal: Error: some packages failed to install:
rfc3339-1.0.2 failed during the building phase. The exception was:
ExitFailure 1