On Nov 21, 2006, at 2:24 PM, Tim Newsham wrote:
Can anyone tell me why I get a type error in the following code? I have to define liftA2 twice to avoid the type error. Both times its defined identically but with different type signature. If I use the original liftA2 in place of liftA2' I get:
whyerror.lhs:36:25: Ambiguous type variable `a' in the constraint: `Arrow a' arising from use of `>>>' at whyerror.lhs:36:25-27 Possible cause: the monomorphism restriction applied to the following: liftA2' :: forall b a1 b1 c. (a1 -> b1 -> c) -> a b a1 -> a b b1 -> a b c (bound at whyerror.lhs:36:1) unsplit' :: forall a1 b c. (a1 -> b -> c) -> a (a1, b) c (bound at whyerror.lhs:34:1) split' :: forall b. a b (b, b) (bound at whyerror.lhs:33:1) Probable fix: give these definition(s) an explicit type signature or use -fno-monomorphism-restriction
I'm not sure I understand your problem. If I comment out split', unsplit' and liftA2', your program compiles and executes. Without signatures, MR kicks in and gives the error above (which recommends you give signatures ;-) ) However, you've got type signatures, and the foul MR beast is slain, so the problem appears solved... [snip code]
Tim Newsham http://www.thenewsh.com/~newsham/
Rob Dockins Speak softly and drive a Sherman tank. Laugh hard; it's a long way to the bank. -- TMBG