有没有办法根据关联的类型同义词定义类型同义词?(不确定我是否有正确的术语。)
{-# LANGUAGE TypeFamilies #-}
class Reproductive a where
-- | A sequence of genetic information for an agent.
type Strand a
-- | Full set (both strands) of genetic information for an organism.
type Genome a = (Strand a, Strand a)
这是我收到的错误消息。
λ> :l stackOverflow.hs
[1 of 1] Compiling Main ( stackOverflow.hs, interpreted )
stackOverflow.hs:9:8: error:
‘Genome’ is not a (visible) associated type of class ‘Reproductive’
|
9 | type Genome a = (Strand a, Strand a)
| ^^^^^^
Failed, no modules loaded.
我可以在(Strand a, Strand a)
任何地方使用,但使用Genome a
.
您可以与类分开定义类型同义词:
{-# LANGUAGE TypeFamilies #-}
-- | Full set (both strands) of genetic information for an organism.
type Genome a = (Strand a, Strand a)
class Reproductive a where
-- | A sequence of genetic information for an agent.
type Strand a
或者,如果您希望能够为某些实例覆盖它,那么您可以像这样定义它:
{-# LANGUAGE TypeFamilies #-}
class Reproductive a where
-- | A sequence of genetic information for an agent.
type Strand a
-- | Full set (both strands) of genetic information for an organism.
type Genome a
type Genome a = (Strand a, Strand a)
这似乎是多余的,但您可以将第一type Genome a
行视为签名,将第二行视为默认实现。在这种情况下,签名是简单type Genome a :: *
或type Genome a
短期的,但它可以比变得更加复杂。
本文收集自互联网,转载请注明来源。
如有侵权,请联系 [email protected] 删除。
我来说两句