Or rather, you can just say do { return something } or do { return $ something } of "something" is a more complicated expression. On Fri, Oct 23, 2015 at 10:16 AM Rein Henrichs wrote:

You can't transform an IO String into a String. This is one of the purposes of monads: to make it possible to work with things like IO, where it is impossible to turn an IO a into an a. The result of performing an IO action can be *bound* using (>>=) or <- in do notation so that the String is available for the rest of the computation:

do f <- readFile "ctrl.txt" Right r <- parseCtrl f cherchectrl r "A01"

Note that there's no need to wrap identifiers in (): (r) is the same as r, (rez) is the same as rez. And there's no need to say do { let r = something; return r }. You can just say do { something }.

On Fri, Oct 23, 2015 at 8:32 AM chanti houda wrote:

...

Hello, I'm writing a Haskell code which consists to read a text file, parse it and thansform the parsing result on a specific language. I have a function *affiche *which takes a data type Ctrl and returns a String. This is the transformation funtion. I have also anothe function parsctrl, which parse the contents of a text file ("ctrl.txt") and after looks for a specific value ("A01") in the parse result (function *c**herchectrl*). I need to use the result of the *parsectrl *function in another function *fc*. The code is composed of three functions

parsectrl = do f <- readFile "ctrl.txt" let Right r = parse parseCtrl " " f let rez =cherchectrl ( r) "A01" return (rez)

fc[] =[] fc((door,[(all,v1),(alt,v2),(lint,v3),(w,v4),(r,v5),(loc,v6),( etat,v7),(ruin,v8)]):ls ) = ("&OUV ID='"++door ++"', ALLEGE="++show((moi v1)/1000)++", LINTEAU="++show((moi v3)/1000)++", LARGEUR="++show((moi v4)/1000)++", COEF=0.7, ALT="++show((moi v2)/1000)++", LOCIDS='"++v6++"', CTRLID='"++ v7++"', CTRLID_RUIN='"++ v8++" /" ++"\n" ++"&CTRL ID='"++v7++"', " ++ "ON_INI=.FALSE., DURATION=0 / \n"++"&CTRL ID='"++v8++"', LOCID='"++ ((parses("'"++v6++"'"))!!0) ++ *affiche(parsectrl)*++ " / \n\n" )++fc(ls)

The parsectrl returns an IO String, but the function affiche needs a String as input and even when I tried to adapt the affiche function to take an IO String -> String I can't. the result of fc must be a String too.

The IO String comes from the parsectrl function. Can you help me to solve this problem: how can I transform an IO String to a String.

Thank you by advance.

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