修复由有界数据类型索引的数组？

I want to achieve something similar to the bounded arrays in the standard array package but using repa arrays.

我想在标准数组包中实现类似于有界数组的东西，但是使用了数组。

What is the nice and clean way to achieve this?

实现这一目标的好方法是什么？

This is what I tried, but there must be a better way than wrapping everything in custom functions that check for bounds:

这是我尝试过的，但必须有一个比检查边界的自定义函数中包装所有内容更好的方法：

import  Data.Array.Repa

data C = A | F | L deriving (Eq,Enum,Ord,Bounded,Show)

data Ballot c = Ballot {
    vote::Array U (Z :. Int) Int
    } deriving Show

mkBallot::(Eq c ,Enum c,Ord c, Bounded c, Show c) => c -> Ballot c
mkBallot c = Ballot $ fromListUnboxed (Z :. max) (genSc c)
where
    max = (fromEnum (maxBound `asTypeOf` c)) + 1

genSc::(Eq c,Enum c,Ord c,Bounded c,Show c) => c -> [Int]
genSc c = [ f x | x <- enumFrom (minBound `asTypeOf` c) , let f v = if x == c then 1 else 0]

showScore c b = index (vote b) (Z :. ((fromEnum c)))

Also I have tried to derive a Shape instance for (sh :. C) but to no avail, I can't really get my head around on how to implement some of the interfaces declared in the Shape class for my data type. I am writing the question with the hope that someone else has a way, but if not, I shall try again. Thank you!

此外，我试图为（sh：.C）派生一个Shape实例，但无济于事，我无法真正了解如何在我的数据类型的Shape类中实现一些声明的接口。我正在写这个问题，希望别人有办法，但如果没有，我会再试一次。谢谢！

1 个解决方案

#1

You can make a shape instance for a wrapper around your bounded enum. I'm not sure this is the best way, but it sort of does what you want, I think.

您可以为有界枚举周围的包装器创建一个形状实例。我不确定这是最好的方式，但我觉得它有点像你想要的那样。

{-# LANGUAGE ScopedTypeVariables  #-}

import Data.Array.Repa

Here we make a shape instance over bounded things. We need an end-of-index for "full" arrays.

在这里，我们在有界的东西上做一个形状实例。我们需要一个“完整”数组的索引结束。

data Idx a = Idx a | EOI
           deriving (Eq, Ord, Show)

fromIdx :: forall a . (Bounded a, Enum a) => Idx a -> Int
fromIdx EOI = fromEnum (maxBound :: a) - fromEnum (minBound :: a) + 1
fromIdx (Idx x) = fromEnum x - fromEnum (minBound :: a)

toIdx ::  forall a . (Bounded a, Enum a) => Int -> Idx a
toIdx i | i < 0 = error "negative index"
toIdx i = case compare i range of
  LT -> Idx $ toEnum (i + fromEnum (minBound :: a))
  EQ -> EOI
  GT -> error "out of range"
  where
    range = fromEnum (maxBound :: a) - fromEnum (minBound :: a) + 1

instance (Bounded a, Enum a, Ord a) => Shape (Idx a) where
  rank _ = 1
  zeroDim = Idx minBound
  unitDim = Idx $ succ minBound
  intersectDim EOI n = n
  intersectDim n EOI = n
  intersectDim (Idx n1) (Idx n2) = Idx $ min n1 n2
  addDim = error "undefined"
  size = fromIdx
  sizeIsValid _ = True
  toIndex _ n = fromIdx n
  fromIndex _ i = toIdx i
  inShapeRange _ _ EOI = error "bad index"
  inShapeRange n1 n2 n = n >= n1 && n <= n2
  listOfShape n = [fromIdx n]
  shapeOfList [i] = toIdx i
  shapeOfList _ = error "unsupported shape"
  deepSeq (Idx n) x = n `seq` x
  deepSeq _ x = x

With that, the ballot part is easy and clean:

这样，选票部分简单易行：

data C = A | F | L deriving (Eq, Enum, Ord, Bounded, Show)

data Ballot c = Ballot { vote :: Array U (Idx c) Int
                       } deriving Show

mkBallot :: (Eq c, Enum c, Ord c, Bounded c, Show c) => c -> Ballot c
mkBallot c = Ballot $ fromListUnboxed EOI vec
  where
    vec = map (fromEnum . (== c)) [minBound .. maxBound]

#1