Haskell-如何在Float和Double之间进行泛化

Question

我有一个简单的类型类，用于表示连续概率分布，只有一个实例。我想写尽可能通用的类型类和公式，这样，例如，我就可以在Float或Double之间进行适当的选择。

这不会编译：

class ContinuousDistribution d where
ppf :: Floating a => d -> a -> a
data Uniform = Uniform
{ lowerBound :: Float
, upperBound :: Float
} deriving (Show)
instance ContinuousDistribution Uniform where
ppf d q = (1.0 - q) * lowerBound d + q * upperBound d

生产

stats.hs:10:27: error:
• Couldn't match expected type ‘a’ with actual type ‘Float’
‘a’ is a rigid type variable bound by
the type signature for:
ppf :: forall a. Floating a => Uniform -> a -> a
at stats.hs:10:5
• In the second argument of ‘(*)’, namely ‘lowerBound d’
In the first argument of ‘(+)’, namely ‘(1.0 - q) * lowerBound d’
In the expression: (1.0 - q) * lowerBound d + q * upperBound d
• Relevant bindings include
q :: a (bound at stats.hs:10:11)
ppf :: Uniform -> a -> a (bound at stats.hs:10:5)
Failed, modules loaded: none.

在类型类声明中指定类型可以编译，但限制我使用Float。

class ContinuousDistribution d where
ppf :: d -> Float -> Float
data Uniform = Uniform
{ lowerBound :: Float
, upperBound :: Float
} deriving (Show)
instance ContinuousDistribution Uniform where
ppf d q = (1.0 - q) * lowerBound d + q * upperBound d

修改typeclass以便根据需要使用Float或Double的规范方法是什么？

Answer 1

让您的分布参数数据结构由Floating实例参数化：

data Uniform a = Uniform
{ lowerBound :: a
, upperBound :: a
} deriving (Show)
class ContinuousDistribution d where
ppf :: Floating a => d a -> a -> a
instance ContinuousDistribution Uniform where
ppf d q = (1.0 - q) * lowerBound d + q * upperBound d