Haskell中的类型演绎是如何工作的?

我自己做的家庭作业是建立一个时钟滴答声发生器,它会给我泊松分布的区间,最终的结果(经过长时间的斗争,我承认)是这样的:

import System.Random
poissonStream :: ( Ord r, Random r, Floating r, RandomGen g) => r -> r -> r -> g -> [r]
poissonStream rate start limit gen 
        | next > limit = [] 
        | otherwise     = next:(poissonStream rate next limit newGen)
        where  (rvalue, newGen) = random gen
               next = start - log(rvalue) / rate  

Ord r “以及” Floating r “?(我本以为会有某种自动继承:”Floating“意味着”Ord“。)

隐含类型定义的路径是什么?” rvalue :: Float 在GHCi,我得到了我所期望的:

*Main System.Random> let (rvalue, newGen) = random (mkStdGen 100)
<interactive>:1:23:
    Ambiguous type variable `t' in the constraint:
      `Random t' arising from a use of `random' at <interactive>:1:23-43
    Probable fix: add a type signature that fixes these type variable(s)

*Main System.Random> let (rvalue, newGen) = random (mkStdGen 100) :: (Float, StdGen)
*Main System.Random> rvalue
0.18520793

请温柔地使用Haskell n00b。