tcfail001.hs:9:warning:
    Duplicated class assertion `A a' in context: `(A a, A a)'
 
tcfail001.hs:9: Couldn't match the type
		    `GHC.-> oakH' against `PrelBase.[]'
    Expected: `oakH -> oakI'
    Inferred: `[takF]'
    In an equation for function `op': `op PrelBase.[] = PrelBase.[]'

Compilation had errors