Question

这在ghci中工作正常：

printRobot (fight killerRobot gentleGiant)

但这会引发“没有要显示的实例”错误，而且我似乎看不出原因。

threeRoundFight a b = 
(\a b -> printRobot (fight a b))

这是错误：

• No instance for (Show
                     ((((t40, t50, t50) -> t50) -> t60)
                      -> (((t20, t10, t60) -> ((t20, t10, t60) -> t0) -> t0)
                          -> (([Char], a10, a0) -> [Char]) -> t30)
                      -> t30))
    arising from a use of ‘print’
    (maybe you haven't applied a function to enough arguments?)
• In the first argument of ‘print’, namely ‘it’
  In a stmt of an interactive GHCi command: print it

以下是需要考虑的必要功能：

fight aRobot defender = damage defender attack
where attack = if getHP aRobot > 10
            then getAttack aRobot
            else 0

printRobot aRobot = aRobot(\(n,a,h)->n ++ " attack:" ++ (show a) ++ " hp: " ++ (show h))

robot (name,attack,hp) = \message -> message (name,attack,hp)

这里是机器人（我作为参数输入的内容，即killerRobot和gentleGiant）：

killerRobot = robot ("killer",25,200)
gentleGiant = robot ("Mr.Friendly", 10, 300)

您也可以看到，我正在尝试通过嵌套Lambda覆盖机器人，使其成为 3Round 战斗。但是我似乎不明白如果我能从第一场战斗开始的话该如何继续下去。

Answer 1

行

threeRoundFight a b = (\a b -> printRobot (fight a b))

等同于

threeRoundFight x y = (\a b -> printRobot (fight a b))
             -- ^^^ unused variables

（如果启用警告，GHC会帮助您检测到此错误）

这不是您想要的。您可能想要

threeRoundFight = (\a b -> printRobot (fight a b))
-- or
threeRoundFight a b = printRobot (fight a b)

Lambda函数中没有要显示的实例？

1 个答案: