On Dec 21, 2007 4:39 AM, Ronald Guida <[EMAIL PROTECTED]> wrote: > Finally, I tried to define vecLength, but I am getting an error. > > > vecLength :: (Peano s) => Vec s t -> Int > > vecLength _ = pToInt (pGetValue :: s)
The s in (pGetValue :: s) is different from the s in (Peano s). Use the "scoped type variables" extension: vecLength :: forall s. (Peano s) => Vec s t -> Int vecLength _ = pToInt (pGetValue :: s) The forall introduces a scope for s, which type signatures usually do not. Luke > < Could not deduce (Peano s1) from the context () > < arising from a use of `pGetValue' > < Possible fix: > < add (Peano s1) to the context of the polymorphic type `forall s. s' > < In the first argument of `pToInt', namely `(pGetValue :: s)' > < In the expression: pToInt (pGetValue :: s) > < In the definition of `vecLength': > < vecLength _ = pToInt (pGetValue :: s) > > Any suggestions? > -- Ron > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
