So in Haskell 98, would the added constraints result in a type error? - Job
On Tue, Apr 6, 2010 at 5:12 PM, Ross Paterson <r...@soi.city.ac.uk> wrote: > On Tue, Apr 06, 2010 at 03:56:32PM -0400, Job Vranish wrote: > > f _ = undefined > > where > > _ = y :: Int -> Int > > > > y x = undefined > > where > > _ = f x > > Because f and y are mutually recursive, their types are inferred together, > so y gets the type Int -> Int (as given), which forces f :: Int -> a. > > If you add the type signature f :: a -> b, you break the cycle: that > type is used in inferring the type of y (namely a -> b), which is then > used in checking the typeof f. Ditto if you add y :: a -> b instead. > (This is not Haskell 98, but the implementations have done this for > years, and it will be in Haskell 2010.) > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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