[英]Haskell vector type declaration
I'm writing a comparator to pass to sortBy
but I can't get the type declaration right. 我正在编写一个比较器来传递给
sortBy
但我无法获得类型声明。 The input is two Data.Vector
's, each containing two numbers. 输入是两个
Data.Vector
,每个包含两个数字。
-- Comparator to sort a list of individuals by increasing order of fit-0
-- and for individuals with equal fit-0, with increasing order of fit-1
indCmp :: (Ord a, Num a, Vector a) => a -> a -> Ordering
indCmp x y
| (x ! 0) < (y ! 0) = LT
| (x ! 0) > (y ! 0) = GT
| (x ! 1) < (y ! 1) = LT -- Can assume (x ! 0) == (y ! 0) here and beneath
| (x ! 1) > (y ! 1) = GT
| (x ! 1) == (y ! 1) = EQ
GHCI complains: GHCI抱怨:
Expected a constraint, but 'Vector a' has kind '*'
预计有一个约束,但'Vector a'有点'*'
Vector
is a data type, not a class, so your function type should be Vector
是一种数据类型,而不是类,所以你的函数类型应该是
indCmp :: (Ord a, Num a) => Vector a -> Vector a -> Ordering
When I changed this, it compiled for me. 当我改变它时,它为我编译。
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