Resolving dependencies...
Downloading wtk-0.1...
Configuring wtk-0.1...
Building wtk-0.1...
Preprocessing library wtk-0.1...
[1 of 4] Compiling Text.PrettyShow  ( Text/PrettyShow.hs, dist/build/Text/PrettyShow.o )

Text/PrettyShow.hs:78:10:
    Illegal instance declaration for ‘PrettyShow 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 FlexibleInstances if you want to disable this.)
    In the instance declaration for ‘PrettyShow String’
Failed to install wtk-0.1
cabal: Error: some packages failed to install:
wtk-0.1 failed during the building phase. The exception was:
ExitFailure 1