Greg Buchholz wrote: > ...That first article is the strangest. I couldn't reconcile the fact > that if our type signature specifies two arguments, we can pattern > match on three arguments in the function definition. Compare the number > of arguments in the first and second instances... > >> class BuildList a r | r-> a where >> build' :: [a] -> a -> r >> >> instance BuildList a [a] where >> build' l x = reverse$ x:l >> >> instance BuildList a r => BuildList a (a->r) where >> build' l x y = build'(x:l) y
I'm not sure I'm getting your point, but this is just because in the second instance, the second parameter of BuildList is 'a -> r', so the specific type of 'build\'' is '[a] -> a -> (a -> r)' which is just '[a] -> a -> a -> r' (currying at work). Regards, Arie _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
