Yes, it has to do with mutually recursive bindings. If you add a type
signature, you break the mutual recursion. Mutually recursive
functions are type-checked together and then generalised. Similarly,
polymorphic recursion cannot be inferred either, but is possible by
adding a type signature.
HTH
On 6 April 2010 20:56, Job Vranish
Is haskell supposed to always infer the most general type (barring extensions)?
I found a simple case where this is not true:
f _ = undefined where _ = y :: Int -> Int
y x = undefined where _ = f x
Haskell infers the types of 'y' and 'f' as: f :: Int -> a y :: Int -> Int
This confused me at first, but after thinking about it a while it seemed to make sense. But then my friend John pointed out that you can add type sigs for 'f' and 'y': f :: a -> b y :: a -> b and have it still typecheck!
This thoroughly confused me.
Why does haskell not infer the most general type for these functions? Is it a limitation of the algorithm? a limitation of the recursive let binding?
Any insight would be appreciated :)
- Job
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