
tcfail153.hs:6:9:
    Couldn't match type `a' with `Bool'
      `a' is a rigid type variable bound by
          the type signature for f :: a -> [a] at tcfail153.hs:6:1
    In the first argument of `g', namely `x'
    In the expression: g x
    In an equation for `f':
        f x
          = g x
          where
              g y = if y then [] else [...]
