Haskell - 打印数字

Question

我写了以下代码:

module Test where

import Char
import IO

main = do
    str <- readFile "no.txt"
    putStrLn (show(english str))

string2list :: String -> [String]
string2list "" = []
string2list s = words s


english :: String -> Int
english s
    | head (string2list s) == "one"     = 1
    | head (string2list s) == "two"     = 2
    | head (string2list s) == "three"   = 3
    | head (string2list s) == "four"    = 4
    | head (string2list s) == "five"    = 5
    | head (string2list s) == "six"     = 6
    | head (string2list s) == "seven"   = 7
    | head (string2list s) == "eight"   = 8
    | head (string2list s) == "nine"    = 9
    | otherwise                         = error "not match"

在no.txt中:

one
two
three
four
....

在编译并运行代码之后,我得到了结果:

1

但我希望得到:

1
2
3
4
...

代码有什么问题？有帮助吗？谢谢!

Answer 1

strone\ntwo读取时不是字符串列表(它只是一个字符串)readFile.做

main = do
    str <- readFile "no.txt"
    mapM_ (\x -> putStrLn (show(english x))) $ lines str

在你的main代替和使用转换str为列表lines(见文档的行).

Answer 2

这不是你的问题的答案,而是风格的建议.你可以摆脱那些罗嗦head (string2list s)使用模式匹配和替换的东西string2list用words; 两者都完全相同:

english s = case words s of
  "one"   :_ -> 1
  "two"   :_ -> 2
  "three" :_ -> 3
  "four"  :_ -> 4
  "five"  :_ -> 5
  "six"   :_ -> 6 
  "seven" :_ -> 7
  "eight" :_ -> 8 
  "nine"  :_ -> 9
  _          -> error "no match"