向量空间库与标量型约束

Question

import Data.VectorSpace
-- scale a vector with a float
step :: (VectorSpace a) => a -> Float -> a
step x dt = x ^* dt

Could not deduce (Scalar a ~ Float)
from the context (VectorSpace a)
  bound by the type signature for
        step :: VectorSpace a => a -> Float -> a
  at Test.hs:5:9-42 
In the expression: x ^* dt
In an equation for `step': step x dt = x ^* dt

step (1,1) 0.5
step 1 0.5

从本质上说，我希望重用向量空间定义的一些实例。

Answer 1

{-# LANGUAGE GADTs #-}
import Data.VectorSpace

step :: (VectorSpace a, Scalar a ~ Float) => a -> Float -> a
step x dt = x ^* dt