2 tcfail001.hs:9:warning:
3 Duplicated class assertion `A a' in context: `(A a, A a)'
5 tcfail001.hs:9: Couldn't match the type `-> oalM' against `[]'
6 Expected: `oalM -> oalN'
8 In an equation for function `op': `op [] = []'
10 Compilation had errors