如何实现 fromJust 并遍历 Haskell 中的字符串列表
How to implement fromJust and iterate over a list of strings in Haskell
所以我得到了这些功能:
intercalate' :: [a] -> [[a]] -> [a]
intercalate' xs xss = concat (intersperse' xs xss)
intersperse' :: a -> [a] -> [a]
intersperse' _ [] = []
intersperse' sep (x:xs) = x : prependToAll' sep xs
prependToAll' :: a -> [a] -> [a]
prependToAll' _ [] = []
prependToAll' sep (x:xs) = sep : x : prependToAll' sep xs
encodeWord :: Table -> String -> Maybe Code
encodeWord table str = intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str
对于此数据:
module Types where
data Atom = Beep | Silence
deriving (Eq, Show)
type Code = [Atom]
dit, dah, shortGap, mediumGap :: Code
dit = [Beep, Silence]
dah = [Beep, Beep, Beep, Silence]
shortGap = replicate (3-1) Silence
mediumGap = replicate (7-1) Silence
morseCode :: Char -> Code
morseCode 'A' = dit ++ dah
morseCode 'B' = dah ++ dit ++ dit ++ dit
morseCode 'C' = dah ++ dit ++ dah ++ dit
morseCode 'D' = dah ++ dit ++ dit
morseCode 'E' = dit
morseCode 'F' = dit ++ dit ++ dah ++ dit
morseCode 'G' = dah ++ dah ++ dit
morseCode 'H' = dit ++ dit ++ dit ++ dit
morseCode 'I' = dit ++ dit
morseCode 'J' = dit ++ dah ++ dah ++ dah
morseCode 'K' = dah ++ dit ++ dah
morseCode 'L' = dit ++ dah ++ dit ++ dit
morseCode 'M' = dah ++ dah
morseCode 'N' = dah ++ dit
morseCode 'O' = dah ++ dah ++ dah
morseCode 'P' = dit ++ dah ++ dah ++ dit
morseCode 'Q' = dah ++ dah ++ dit ++ dah
morseCode 'R' = dit ++ dah ++ dit
morseCode 'S' = dit ++ dit ++ dit
morseCode 'T' = dah
morseCode 'U' = dit ++ dit ++ dah
morseCode 'V' = dit ++ dit ++ dit ++ dah
morseCode 'W' = dit ++ dah ++ dah
morseCode 'X' = dah ++ dit ++ dit ++ dah
morseCode 'Y' = dah ++ dit ++ dah ++ dah
morseCode 'Z' = dah ++ dah ++ dit ++ dit
morseCode '1' = dit ++ dah ++ dah ++ dah ++ dah
morseCode '2' = dit ++ dit ++ dah ++ dah ++ dah
morseCode '3' = dit ++ dit ++ dit ++ dah ++ dah
morseCode '4' = dit ++ dit ++ dit ++ dit ++ dah
morseCode '5' = dit ++ dit ++ dit ++ dit ++ dit
morseCode '6' = dah ++ dit ++ dit ++ dit ++ dit
morseCode '7' = dah ++ dah ++ dit ++ dit ++ dit
morseCode '8' = dah ++ dah ++ dah ++ dit ++ dit
morseCode '9' = dah ++ dah ++ dah ++ dah ++ dit
morseCode '0' = dah ++ dah ++ dah ++ dah ++ dah
morseCode _ = undefined -- Avoid warnings
type Table = [(Char, Code)]
morseTable :: Table
morseTable = [ (c , morseCode c) | c <- ['A'..'Z']++['0'..'9'] ]
encodeWord
函数按预期工作。
样本:输入:"HELLO"
输出:[Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence]
现在,我正在尝试定义一个新函数:encodeWords。
样本:输入:["HI","THERE"]
输出:[Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence]
到目前为止,我已经做到了。
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList = intercalate' [Silence, Silence, Silence,Silence,Silence,Silence]
<$> mapM (\x -> encodeWord table x ) stringList
我希望最终函数具有类型签名:
Table -> [String] -> Code
对于encodeWord
,我只成功编程了Table -> [String] -> Maybe Code
。我试过像这样使用 fromJust
:
import Data.Maybe
encodeWord :: Table -> String -> Code
encodeWord table str = fromJust (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
这有效,但是,我只能将 Prelude 和 Data.Char 用于我正在编写的程序。
当我尝试时:
fromJust :: HasCallStack => Maybe a -> a
fromJust Nothing = error "Maybe.fromJust: Nothing" -- yuck
fromJust (Just x) = x
type HasCallStack = (?callStack :: CallStack)
encodeWord :: Table -> String -> Code
encodeWord table str = fromJust (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
我刚收到这个错误:
Operator applied to too few arguments: ?
|
59 | type HasCallStack = (?callStack :: CallStack)
| ^
Failed, one module loaded.
有什么简单的方法可以让我自己实现 fromJust
,只需要使用 Data.Char 和 Prelude 吗?
总而言之,我正在尝试自己实现 fromJust
并使此功能正常工作:
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList = intercalate' [Silence, Silence, Silence,Silence,Silence,Silence]
<$> mapM (\x -> encodeWord table x ) stringList
我不确定是否应该 Map
、MapM
或其他东西来将 encodeWord
应用于列表中的每个字符串。之后,encodeWords
应该在输入列表中的每个字符串的输出 Code
之间添加 6 Silence
s。
你写的 fromJust
的定义,直接来自 Data.Maybe
。如果不进行简单的修改,这将无法工作:
fromJust :: Maybe a -> a
fromJust Nothing = error "fromJust: Nothing"
fromJust (Just x) = x
如您所见,fromJust
模式匹配 Maybe
数据类型的构造函数,就像您对 morseCode
.
所做的一样
有关模式匹配的更多信息,请参阅:http://learnyouahaskell.com/syntax-in-functions
如果出现问题,return Nothing
是一个非常可行的错误管理策略,您可以级联它。
最后,你总可以把结果通过fromJust
,如果有非法输入,后果自负。正如 HaskellFreak 所提到的,您的 fromJust
版本看起来不错。
此代码似乎有效:
myFromJust :: Maybe a -> a
myFromJust Nothing = error "Maybe.fromJust: Nothing" -- yuck
myFromJust (Just x) = x
encodeWord :: Table -> String -> Maybe Code
encodeWord table str = (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
在ghci
下测试:
λ>
λ> encodeWord morseTable "ABC"
Just [Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence]
λ>
λ>
λ> encodeWord morseTable "ABC+"
Nothing
λ>
现在正在尝试编写更高级别的函数 encodeWords
:
如果我们从一个简单的 map
结构开始:
λ>
λ> stringList = ["ATTACK","AT","DAWN"]
λ>
λ> :type (map (encodeWord morseTable) stringList)
(map (encodeWord morseTable) stringList) :: [Maybe Code]
λ>
所以我们有一个 [Maybe Code] 对象。鉴于 intercalate'
的类型签名,我们更喜欢 Maybe [Code]
一个。
λ>
λ> :type mapM
mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)
λ>
所以如果类型a
与m b
相同,最左边的函数参数取id
,我们看到mapM
可以交换列表用 Maybe 构造。比如:(m b -> m b) -> t (m b) -> m (t b)
.
λ>
λ> :type (mapM id)
(mapM id) :: (Traversable t, Monad m) => t (m b) -> m (t b)
λ>
λ> :type (mapM id $ map (encodeWord morseTable) stringList)
(mapM id $ map (encodeWord morseTable) stringList) :: Maybe [Code]
λ>
λ>
λ> sil6 = replicate 6 Silence
λ>
λ> :type ((intercalate' sil6) <$> mapM id (map (encodeWord morseTable) stringList))
((intercalate' sil6) <$> mapM id (map (encodeWord morseTable) stringList))
:: Maybe [Atom]
λ>
所以这可能是 encodeWords
的有效代码:
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList =
let sil6 = replicate 6 Silence
in
intercalate' sil6
<$> (mapM id $ map (encodeWord table) stringList)
在ghci
下测试:
λ>
λ> length $ myFromJust (encodeWords morseTable stringList)
112
λ> (encodeWords morseTable stringList)
Just [Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence]
λ>
请注意,在这种情况下,mapM id
与库函数 sequence :: Monad m => t (m a) -> m (t a) 相同,后者肯定在 Prelude 集中。
为了全面公开,Prelude 库还包含一个 traverse 函数,它是 sequence
和 map
之间的调情。所以你可以像这样写一个更优雅的 encodeWords
版本:
encodeWords2 :: Table -> [String] -> Maybe Code
encodeWords2 table stringList =
let sil6 = replicate 6 Silence
in intercalate' sil6 <$> traverse (encodeWord table) stringList
所以我得到了这些功能:
intercalate' :: [a] -> [[a]] -> [a]
intercalate' xs xss = concat (intersperse' xs xss)
intersperse' :: a -> [a] -> [a]
intersperse' _ [] = []
intersperse' sep (x:xs) = x : prependToAll' sep xs
prependToAll' :: a -> [a] -> [a]
prependToAll' _ [] = []
prependToAll' sep (x:xs) = sep : x : prependToAll' sep xs
encodeWord :: Table -> String -> Maybe Code
encodeWord table str = intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str
对于此数据:
module Types where
data Atom = Beep | Silence
deriving (Eq, Show)
type Code = [Atom]
dit, dah, shortGap, mediumGap :: Code
dit = [Beep, Silence]
dah = [Beep, Beep, Beep, Silence]
shortGap = replicate (3-1) Silence
mediumGap = replicate (7-1) Silence
morseCode :: Char -> Code
morseCode 'A' = dit ++ dah
morseCode 'B' = dah ++ dit ++ dit ++ dit
morseCode 'C' = dah ++ dit ++ dah ++ dit
morseCode 'D' = dah ++ dit ++ dit
morseCode 'E' = dit
morseCode 'F' = dit ++ dit ++ dah ++ dit
morseCode 'G' = dah ++ dah ++ dit
morseCode 'H' = dit ++ dit ++ dit ++ dit
morseCode 'I' = dit ++ dit
morseCode 'J' = dit ++ dah ++ dah ++ dah
morseCode 'K' = dah ++ dit ++ dah
morseCode 'L' = dit ++ dah ++ dit ++ dit
morseCode 'M' = dah ++ dah
morseCode 'N' = dah ++ dit
morseCode 'O' = dah ++ dah ++ dah
morseCode 'P' = dit ++ dah ++ dah ++ dit
morseCode 'Q' = dah ++ dah ++ dit ++ dah
morseCode 'R' = dit ++ dah ++ dit
morseCode 'S' = dit ++ dit ++ dit
morseCode 'T' = dah
morseCode 'U' = dit ++ dit ++ dah
morseCode 'V' = dit ++ dit ++ dit ++ dah
morseCode 'W' = dit ++ dah ++ dah
morseCode 'X' = dah ++ dit ++ dit ++ dah
morseCode 'Y' = dah ++ dit ++ dah ++ dah
morseCode 'Z' = dah ++ dah ++ dit ++ dit
morseCode '1' = dit ++ dah ++ dah ++ dah ++ dah
morseCode '2' = dit ++ dit ++ dah ++ dah ++ dah
morseCode '3' = dit ++ dit ++ dit ++ dah ++ dah
morseCode '4' = dit ++ dit ++ dit ++ dit ++ dah
morseCode '5' = dit ++ dit ++ dit ++ dit ++ dit
morseCode '6' = dah ++ dit ++ dit ++ dit ++ dit
morseCode '7' = dah ++ dah ++ dit ++ dit ++ dit
morseCode '8' = dah ++ dah ++ dah ++ dit ++ dit
morseCode '9' = dah ++ dah ++ dah ++ dah ++ dit
morseCode '0' = dah ++ dah ++ dah ++ dah ++ dah
morseCode _ = undefined -- Avoid warnings
type Table = [(Char, Code)]
morseTable :: Table
morseTable = [ (c , morseCode c) | c <- ['A'..'Z']++['0'..'9'] ]
encodeWord
函数按预期工作。
样本:输入:"HELLO"
输出:[Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence]
现在,我正在尝试定义一个新函数:encodeWords。
样本:输入:["HI","THERE"]
输出:[Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence]
到目前为止,我已经做到了。
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList = intercalate' [Silence, Silence, Silence,Silence,Silence,Silence]
<$> mapM (\x -> encodeWord table x ) stringList
我希望最终函数具有类型签名:
Table -> [String] -> Code
对于encodeWord
,我只成功编程了Table -> [String] -> Maybe Code
。我试过像这样使用 fromJust
:
import Data.Maybe
encodeWord :: Table -> String -> Code
encodeWord table str = fromJust (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
这有效,但是,我只能将 Prelude 和 Data.Char 用于我正在编写的程序。
当我尝试时:
fromJust :: HasCallStack => Maybe a -> a
fromJust Nothing = error "Maybe.fromJust: Nothing" -- yuck
fromJust (Just x) = x
type HasCallStack = (?callStack :: CallStack)
encodeWord :: Table -> String -> Code
encodeWord table str = fromJust (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
我刚收到这个错误:
Operator applied to too few arguments: ?
|
59 | type HasCallStack = (?callStack :: CallStack)
| ^
Failed, one module loaded.
有什么简单的方法可以让我自己实现 fromJust
,只需要使用 Data.Char 和 Prelude 吗?
总而言之,我正在尝试自己实现 fromJust
并使此功能正常工作:
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList = intercalate' [Silence, Silence, Silence,Silence,Silence,Silence]
<$> mapM (\x -> encodeWord table x ) stringList
我不确定是否应该 Map
、MapM
或其他东西来将 encodeWord
应用于列表中的每个字符串。之后,encodeWords
应该在输入列表中的每个字符串的输出 Code
之间添加 6 Silence
s。
你写的 fromJust
的定义,直接来自 Data.Maybe
。如果不进行简单的修改,这将无法工作:
fromJust :: Maybe a -> a
fromJust Nothing = error "fromJust: Nothing"
fromJust (Just x) = x
如您所见,fromJust
模式匹配 Maybe
数据类型的构造函数,就像您对 morseCode
.
有关模式匹配的更多信息,请参阅:http://learnyouahaskell.com/syntax-in-functions
如果出现问题,return Nothing
是一个非常可行的错误管理策略,您可以级联它。
最后,你总可以把结果通过fromJust
,如果有非法输入,后果自负。正如 HaskellFreak 所提到的,您的 fromJust
版本看起来不错。
此代码似乎有效:
myFromJust :: Maybe a -> a
myFromJust Nothing = error "Maybe.fromJust: Nothing" -- yuck
myFromJust (Just x) = x
encodeWord :: Table -> String -> Maybe Code
encodeWord table str = (intercalate' [Silence, Silence]
<$> mapM (\x -> lookup x table) str)
在ghci
下测试:
λ>
λ> encodeWord morseTable "ABC"
Just [Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence]
λ>
λ>
λ> encodeWord morseTable "ABC+"
Nothing
λ>
现在正在尝试编写更高级别的函数 encodeWords
:
如果我们从一个简单的 map
结构开始:
λ>
λ> stringList = ["ATTACK","AT","DAWN"]
λ>
λ> :type (map (encodeWord morseTable) stringList)
(map (encodeWord morseTable) stringList) :: [Maybe Code]
λ>
所以我们有一个 [Maybe Code] 对象。鉴于 intercalate'
的类型签名,我们更喜欢 Maybe [Code]
一个。
λ>
λ> :type mapM
mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b)
λ>
所以如果类型a
与m b
相同,最左边的函数参数取id
,我们看到mapM
可以交换列表用 Maybe 构造。比如:(m b -> m b) -> t (m b) -> m (t b)
.
λ>
λ> :type (mapM id)
(mapM id) :: (Traversable t, Monad m) => t (m b) -> m (t b)
λ>
λ> :type (mapM id $ map (encodeWord morseTable) stringList)
(mapM id $ map (encodeWord morseTable) stringList) :: Maybe [Code]
λ>
λ>
λ> sil6 = replicate 6 Silence
λ>
λ> :type ((intercalate' sil6) <$> mapM id (map (encodeWord morseTable) stringList))
((intercalate' sil6) <$> mapM id (map (encodeWord morseTable) stringList))
:: Maybe [Atom]
λ>
所以这可能是 encodeWords
的有效代码:
encodeWords :: Table -> [String] -> Maybe Code
encodeWords table stringList =
let sil6 = replicate 6 Silence
in
intercalate' sil6
<$> (mapM id $ map (encodeWord table) stringList)
在ghci
下测试:
λ>
λ> length $ myFromJust (encodeWords morseTable stringList)
112
λ> (encodeWords morseTable stringList)
Just [Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Silence,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Silence,Beep,Beep,Beep,Silence,Beep,Beep,Beep,Silence,Silence,Silence,Beep,Beep,Beep,Silence,Beep,Silence]
λ>
请注意,在这种情况下,mapM id
与库函数 sequence :: Monad m => t (m a) -> m (t a) 相同,后者肯定在 Prelude 集中。
为了全面公开,Prelude 库还包含一个 traverse 函数,它是 sequence
和 map
之间的调情。所以你可以像这样写一个更优雅的 encodeWords
版本:
encodeWords2 :: Table -> [String] -> Maybe Code
encodeWords2 table stringList =
let sil6 = replicate 6 Silence
in intercalate' sil6 <$> traverse (encodeWord table) stringList