On Thu, Jul 23, 2009 at 9:01 PM, wren ng thornton
John Lask wrote:
Can anyone explain the theoretical reason for this limitation, ie other than it is a syntactical restriction, what would it take to lift this restriction ?
There are a couple of theoretical concerns, mainly that full type-level lambdas can lead down a rocky path (though simple combinators like `flip` and `const` are fine, and that's all we'd need for most cases). But by and large it's just a syntactic restriction.
I wouldn't say it's "just" a syntactic restriction. I'm pretty sure
unrestricted type lambdas are incompatible with Haskell's class
system. Otherwise, you might end up with Functor instances for /\b.
(a,b) and /\a. (a,b), at which point fmap (+1) (1,2) is ambiguous.
--
Dave Menendez