Re: [Haskell-cafe] What is a rigid type variable?

"Luke Palmer" writes:

On Mon, Jun 23, 2008 at 5:58 AM, Luke Palmer wrote:

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On Mon, Jun 23, 2008 at 3:26 AM, Xiao-Yong Jin wrote:

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Hi all,

I'm writing a short function as follows, but I'm not able to find a suitable type signature for `go'. It uses Numeric.LinearAlgebra from hmatrix.

-- | Map each element in a vector to vectors and thus form a matrix -- | row by row mapVecToMat :: (Element a, Element b) => (a -> Vector b) -> Vector a -> Matrix b mapVecToMat f v = fromRows $ go (d - 1) [] where d = dim v go :: Element b => Int -> [Vector b] -> [Vector b] go 0 vs = f (v @> 0) : vs go !j !vs = go (j - 1) (f (v @> j) : vs)

If you want to give a type signature for 'go', you need a GHC extension called ScopeTypeVariables (IIRC).

I was indeed correct on the name of this extension, but it would be no help to you to know this since I made a typo :-)

The extension is called ScopedTypeVaraibles.

You probably already know that this can be enabled with:

{-# LANGUAGE ScopedTypeVariables #-}

Luke

Thanks for the explanation. I guess it's just easier for me not to give any type signature to `go', since ghc should do the type inference quite nicely and reliably. X-Y -- c/* __o/* <\ * (__ */\ <