Generics 编译/修复monadiccp类型错误

如果有人能通过编译monadiccp来帮助我研究这个问题，我将不胜感激。有一个打字问题我不明白

复制步骤

• 安装合理的ghc最新版本；我有7.0.3

• cabal安装Monatron

• cabal解包monadiccp

• ghci控制/CP/ComposableTransformers.hs

我得到这个错误

Control/CP/ComposableTransformers.hs:246:31:
    Couldn't match expected type `Tree solver0 a1 -> Tree solver0 a1'
                with actual type `forall a2. Tree solver a2 -> Tree solver a2'
    Expected type: Tree solver0 a1 -> Tree solver0 a1
      Actual type: Bound solver
    In the second argument of `BBP', namely `bound''
    In the second argument of `($)', namely `BBP (v + 1) bound''
Failed, modules loaded: Control.CP.Transformers, Control.CP.SearchTree, Control.CP.Solver, Control.CP.Queue, Control.CP.Debug, Control.CP.PriorityQueue, Control.Mixin.Mixin.

这是一个奇怪的观察。如果有人改变了这条线

   continue $ BBP (v + 1) bound' 

以错误中给定的类型为特征

   continue $ BBP (v + 1) (undefined :: Tree solver0 a1 -> Tree solver0 a1)

然后它就工作了，但是如果引入一个伪变量

   let x = (undefined :: Tree solver0 a1 -> Tree solver0 a1)
   continue $ BBP (v + 1) x

类型错误变得更加难以理解（我可能需要正式学习类型）

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如果您能了解情况（包括解决问题），我们将不胜感激。我不久前给开发人员发了一封电子邮件，但他没有回复。

我不是100%确定发生了什么，只是简单地手动重写do块就可以为我编译了：

  returnCT (CBBST newBound) (BBP v bound) continue exit =
    newBound >>= continue . BBP (v + 1)

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我可以通过稍微丑化一些类型定义来编译

ComposableTransformers.hs

，如下所示：

newtype CBranchBoundST solver a = CBBST (NewBound solver a)
data    BBEvalState solver a  = BBP Int (Bound solver a)

type Bound    solver a  = Tree solver a -> Tree solver a
type NewBound solver a  = solver (Bound solver a)

instance (Solver solver) => CTransformer (CBranchBoundST solver a)
where
  type CEvalState (CBranchBoundST solver a) = BBEvalState solver a

基本上，我只是将一个类型变量

a

穿过这些定义。我确信修改后的代码与原始代码的意图是一致的

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不幸的是，正如最初的问题提问者所说，出现了许多其他编译错误。

太好了，非常感谢！看起来还有很多错误。。。这是一个非常奇怪的问题。

newtype CBranchBoundST solver a = CBBST (NewBound solver a)
data    BBEvalState solver a  = BBP Int (Bound solver a)

type Bound    solver a  = Tree solver a -> Tree solver a
type NewBound solver a  = solver (Bound solver a)

instance (Solver solver) => CTransformer (CBranchBoundST solver a)
where
  type CEvalState (CBranchBoundST solver a) = BBEvalState solver a