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我在Haskell 寫程序這裏是代碼奇怪的行爲讀取文件
module Main
where
import IO
import Maybe
import Control.Monad.Reader
--il mio environment consiste in una lista di tuple/coppie chiave-valore
data Environment = Env {variables::[(String,String)]}deriving (Show)
fromEnvToPair :: Environment-> [(String,String)]
fromEnvToPair (Env e)= e
estrai' x d
|length x==0=[]
|otherwise=estrai x d
estrai (x:xs) d
| (x:xs)=="" =[]
| x== d=[]
| otherwise = x:(estrai xs d)
--estrae da una stringa tutti i caratteri saino a d
conta' x d n
| length x==0 = 0
|otherwise = conta x d n
conta (x:xs) d n
| x== d=n
| otherwise = (conta xs d (n+1))
primo (a,b,c)=a
secondo (a,b,c)=b
terzo (a,b,c)=c
estraifrom x d n
|n>=(length x) =[]
| x!!n==d = []
|otherwise = x!!n:(estraifrom x d (n+1))
readerContent :: Reader Environment Environment
readerContent =do
content <- ask
return (content)
-- resolve a template into a string
resolve :: [Char]-> Reader Environment (String)
resolve key= do
varValue <- asks (lookupVar key)
return $ maybe "" id varValue
maketuple x =(k,v,l) where
k= (estrai' x ':')--usare estrai'
v=estraifrom x ';' (conta' x ':' 1)
l= (length k)+(length v)+2 --è l'offset dovuto al; e al :
makecontext x
| length x==0 = []
| (elem ':' x)&&(elem ';' x)==False = []
|otherwise= (k,v):makecontext (drop l x) where
t= maketuple x
k= primo t
v= secondo t
l= terzo t
doRead filename = do
bracket(openFile filename ReadMode) hClose(\h -> do
contents <- hGetContents h
return contents
let cont=makecontext contents
putStrLn (take 100 contents)
return (contents))
-- putStrLn (snd (cont!!1)))
-- putStrLn (take 100 contents))
-- estrae i caratteri di una stringa dall'inizio fino al carattere di controllo
-- aggiungere parametri to the environment
-- estrae i caratteri di una stringa dall'inizio fino al carattere di controllo
-- aggiungere parametri to the environment
-- lookup a variable from the environment
lookupVar :: [Char] -> Environment -> Maybe String
lookupVar name env = lookup name (variables env)
lookup' x t=[v| (k,v)<-t,k==x]
fromJust' :: Maybe a -> a
fromJust' (Just x) = x
fromJust' Nothing = error "fromJust: Nothing"
main = do
file<- doRead "context.txt"-- leggo il contesto
let env= Env(makecontext file) -- lo converto in Environment
let c1= fromEnvToPair(runReader readerContent env)
putStrLn(fromJust'(lookupVar "user" env))
--putStrLn ((lookup' "user" (fromEnvToPair env))!!0)-- read the environment
--putStrLn ("user"++ (fst (c1!!1)))
putStrLn ("finito")
--putStrLn("contesto" ++ (snd(context!!1)))
我想要做的就是讀取文件在格式化的內容和環境puting它，以及它閱讀文件，並做所有其他的東西，只有在doRead有 putStrLn（取100內容） 否則我不能拿信，有人知道爲什麼嗎？ 我不想離開那一行，如果我不知道爲什麼 在此先感謝 在此先感謝