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haskell catMaybes用法及代碼示例

Haskell語言Maybe模塊中函數catMaybes的用法及代碼示例。

用法類型:

[Maybe a] -> [a]

從Maybe列表創建Just值列表

示例1:

源碼:

a = [(1,'A'),(2,'B'),(3,'C')]
輸入:
catMaybes [lookup 0 a, lookup 1 a, lookup 3 a, lookup 12 a]
         
輸出:
"AC"
         

示例2:

源碼:

b = [(1,11),(2,22),(3,33)]
輸入:
catMaybes [lookup 0 b, lookup 1 b, lookup 3 b, lookup 12 b]
         
輸出:
[11,33]
         

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