haskell列表列出模式匹配

Question

这是我的代码:

newcell :: [Cell] -> [Cell]
newcell [Cell {cellPosition = cp, cellState = cs}] 
= [Cell {cellPosition = cp, cellState = (nextCellState cs)}]

nextCellState 只是一个功能,但它说不能匹配模式.

src/StudentSources/LangtonsAnt.hs:141:1: Warning:
Pattern match(es) are non-exhaustive
In an equation for ‘newcell’:
    Patterns not matched:
        []
        (Cell _ _) : (_ : _)

Answer 1

您只匹配列表中单个单元格的模式.再看一下错误消息.它会准确地告诉您需要匹配的模式.

空列表:

[]

以及列表中多个Cell的模式:

(Cell _ _) : (_ : _)