Re: [Haskell-cafe] using type variables in type declarations inside function

Thanks! By the way, why do I sometimes have to use forall, and sometimes not? I'm also learning Purescript, and I noticed that the examples use 'forall' in every case. Why would it be different with Purescript? D On Thu, Apr 12, 2018 at 12:51 PM, Brandon Allbery wrote:

On Thu, Apr 12, 2018 at 3:47 PM, Dennis Raddle wrote:

...

myFunc :: a -> b -> c myFunc x y z = ... where helper :: a -> [b] helper xx = ...

Notice that I'm attempting to declare 'helper' using my type variables. I've noticed that this results in an error. Is this actually possible, and how?

You need the ScopedTypeVariables extension, *and* to "declare" the type variables whose scope is to be extended with an explicit "forall" in the signature.

-- brandon s allbery kf8nh sine nomine associates allbery.b@gmail.com ballbery@sinenomine.net unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net