[英]Redesign of Haskell type classes
在得到一些帮助后,理解我试图编译代码的问题,在这个问题中( 麻烦理解GHC关于模糊性的抱怨 )Ness会建议我重新设计我的类型类以避免我不满意的解决方案。
有问题的类型是这些:
class (Eq a, Show a) => Genome a where
crossover :: (Fractional b) => b -> a -> a -> IO (a, a)
mutate :: (Fractional b) => b -> a -> IO a
develop :: (Phenotype b) => a -> b
class (Eq a, Show a) => Phenotype a where
--In case of Coevolution where each phenotype needs to be compared to every other in the population
fitness :: [a] -> a -> Int
genome :: (Genome b) => a -> b
我正在尝试在Haskell中创建一个可扩展的进化算法,它应该支持不同的Genomes
和Phenotypes
。 例如,一个Genome
可能是一个阵列,另一个可能是一个整数列表, Phenotypes
也将不同于一个代表部队运动的双重列表http://en.wikipedia.org/wiki/Colonel_Blotto ,或者它可以代表人工神经网络。
由于Phenotype
是从Genome
开发的,所使用的方法必须是完全可互换的,并且一个Genome
类应该能够通过提供不同的开发方法来支持多个Phenotypes
(这可以在代码中静态完成,而不必动态完成)在运行时)。
在大多数情况下,使用这些类型类的代码应该幸福地不知道所使用的特定类型,这就是让我提出上述问题的原因。
我想要适应这些类型类的一些代码是:
-- |Full generational replacement selection protocol
fullGenerational :: (Phenotype b) =>
(Int -> [b] -> IO [(b, b)]) -> --Selection mechanism
Int -> --Elitism
Int -> --The number of children to create
Double -> --Crossover rate
Double -> --Mutation rate
[b] -> --Population to select from
IO [b] --The new population created
fullGenerational selection e amount cross mute pop = do
parents <- selection (amount - e) pop
next <- breed parents cross mute
return $ next ++ take e reverseSorted
where reverseSorted = reverse $ sortBy (fit pop) pop
breed :: (Phenotype b, Genome a) => [(b, b)] -> Double -> Double -> IO [b]
breed parents cross mute = do
children <- mapM (\ (dad, mom) -> crossover cross (genome dad) (genome mom)) parents
let ch1 = map fst children ++ map snd children
mutated <- mapM (mutate mute) ch1
return $ map develop mutated
我知道必须更改此代码并且必须添加新的约束,但我想要使用类型类来显示我想到的一些代码。 例如,上面的完整世代替代品不需要知道任何关于底层Genome
正常运作; 它只需要知道Phenotypes
可以产生产生它的Genome
,以便它可以将它们一起繁殖并创造新的孩子。 fullGenerational
的代码应尽可能通用,这样一旦设计了新的Phenotype
或创建了更好的Genome
,就不需要更改它。
如何更改上面的类型类以避免我遇到类型类歧义的问题,同时在一般EA代码中保留我想要的属性(应该是可重用的)?
“它只需要知道表型可以产生产生它的基因组”
这意味着Phenotype实际上是两种类型的关系,另一种是用于产生给定表型的基因组类型:
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
import Data.List (sortBy)
class (Eq a, Show a) => Genome a where
crossover :: (Fractional b) => b -> a -> a -> IO (a, a)
mutate :: (Fractional b) => b -> a -> IO a
develop :: (Phenotype b a) => a -> b
class (Eq a, Show a, Genome b) => Phenotype a b | a -> b where
-- In case of Coevolution where each phenotype needs to be compared to
-- every other in the population
fitness :: [a] -> a -> Int
genome :: a -> b
breed :: (Phenotype b a, Genome a) => [(b, b)] -> Double -> Double -> IO [b]
breed parents cross mute = do
children <- mapM (\(dad, mom)-> crossover cross (genome dad) (genome mom))
parents
let ch1 = map fst children ++ map snd children
mutated <- mapM (mutate mute) ch1
return $ map develop mutated
-- |Full generational replacement selection protocol
fullGenerational :: (Phenotype b a, Genome a) =>
(Int -> [b] -> IO [(b, b)]) -> --Selection mechanism
Int -> --Elitism
Int -> --The number of children to create
Double -> --Crossover rate
Double -> --Mutation rate
[b] -> --Population to select from
IO [b] --The new population created
fullGenerational selection e amount cross mute pop = do
parents <- selection (amount - e) pop
next <- breed parents cross mute
return $ next ++ take e reverseSorted
where reverseSorted = reverse $ sortBy (fit pop) pop
fit pop a b = LT -- dummy function
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