Resolving dependencies...
Downloading wtk-0.2...
Configuring wtk-0.2...
Building wtk-0.2...
Preprocessing library wtk-0.2...
[1 of 4] Compiling Text.PrettyShow  ( Text/PrettyShow.hs, dist/build/Text/PrettyShow.o )
[2 of 4] Compiling Text.WtkParser   ( Text/WtkParser.hs, dist/build/Text/WtkParser.o )
[3 of 4] Compiling Text.Calculator  ( Text/Calculator.hs, dist/build/Text/Calculator.o )

Text/Calculator.hs:37:21:
    Could not deduce (Eq a) arising from a use of `=='
    from the context (Num a)
      bound by the instance declaration at Text/Calculator.hs:36:10-35
    Possible fix: add (Eq a) to the context of the instance declaration
    In the expression: 3 `f` 2 == 6
    In a stmt of a pattern guard for
                   an equation for `show':
      3 `f` 2 == 6
    In an equation for `show':
        show f
          | 3 `f` 2 == 6 = "*"
          | 3 `f` 2 == 5 = "+"
          | 3 `f` 2 == 1 = "-"
          | 3 `f` 2 == 8 = "^"
          | otherwise = "/"
Failed to install wtk-0.2
cabal: Error: some packages failed to install:
wtk-0.2 failed during the building phase. The exception was:
ExitFailure 1