haskell - 方程有不同数量的参数

Question

我创建了这些数据类型来表示吉他标签，并且我正在尝试编写 show 函数将它们打印为真正的吉他标签。 数据不是我的专长，我在匹配类型时遇到了困难。

错误是

Equations for `show' have different numbers of arguments In the instance declaration for GHC.Show.Show Tabs.Chord'

代码:

type Strings = Int

data Fret = None | Note Int

instance Show Fret where
  show None = "-"
  show (Note a) = show a

data Chord = EmptyChord Strings | Chord [Fret]

instance Show Chord where
  show EmptyChord a = init $ take (a * 2) ['-', '\n' ..]
  show Chord (x : xs) = x : '\n' : show xs

Answer 1

第二个实例需要更多括号:

instance Show Chord where
  show (EmptyChord a) = init $ take (a * 2) ['-', '\n' ..]
  show (Chord (x : xs)) = x : '\n' : show xs