4
我有我自己的数据类型,指出:哈斯克尔不在范围内:类型构造函数或类`PushInt”
data Commands = MoveLeft |
MoveRight |
MoveUp |
MoveDown |
IfVertical |
IfHorizontal |
InputChar |
InputInt |
OutputChar |
OutputInt |
OutputNewline |
PushInt Int |
Add |
Sub |
Mult |
Div |
Exp |
Pop |
Dup |
Switch |
Noop |
End
deriving (Show, Eq)
,我有一个功能,与我试图从PushInt
提取数搭配:
extractNum :: PushInt -> Int
extractNum (PushInt n) = n
但是当我尝试运行此,我得到一个错误,指出:
Parser.hs:32:19:
Not in scope: type constructor or class `PushInt'
A data constructor of that name is in scope; did you mean -XDataKinds?
至于我知道我是允许使用此方法从数据中提取字段。我很确定这只是一个非常简单的错误,但任何帮助表示赞赏。