Am Freitag 26 Februar 2010 18:34:35 schrieb Florian Duret:
It seems that both your suggestions have worked ! Thank you very much. But I still can't figure out what went wrong.
Did you change anything besides removing the "do" and "return ()" from the then-branch and insert the "do" in the else-branch? If not, you've been bitten by a somewhat less than obvious aspect of layout - although it's pretty clear with an explanation. A new layout-block isn't opened by a larger indentation, but by the keywords do, let, of and where. So, when you write ... = do xxx if blah then do foo bar else baz zap the "do" after the then opens a new layout-block inside the big do-block, since you didn't insert an explicit brace. The indentation level thereof is determined by the 'f' of "foo", bar is indented to the same level as foo, so it's a new expression in that same block. The else is indented less than the foo, so that ends the inner layout-block and we return to the layout-block of the big do-block. The indentation level thereof is determined by the first 'x', and the "if" is indented to the same level. The else, the baz and the zap are all indented further than the if, so they all belong to the if-expression (as intended). But since there's no "do" after the "else", all that is on one logical line, it's parsed as ... = do xxx if blah then do { foo; bar } else baz zap Not what was intended, but it parses just fine. Now you didn't have baz zap but baz <- bong zap and since we're still having only one logical line for the if-expression, the parser sees that as ... = do xxx if blah then do { foo; bar } else baz <- bong zap But the syntax is pattern <- expression so the parser tries to parse if blah then do { foo; bar } else baz as a pattern. But it doesn't conform to the pattern productions, hence the parse error.
My initial goal was to keep the minimum inside the if ... then ... else statement. Basically, if the list is empty, then stop. If not, then assign the argument to sacFile1, and go on with the rest.
It would be cleanest to have realWork :: FileName -> IO () realWork file = do sacFile1 <- openBinaryFile file ReadMode ... main :: IO () main = do argList <- getArgs case argList of [] -> putStrLn "No filename ..." (f:_) -> realWork f or if null argList then putStrLn "..." else realWork (head argList) , je pense.
Here is what it looks like now: module Main () where
import System.IO import System.Environment(getArgs) import Data.Char(intToDigit)
import SAC_Type import SAC_IO
main :: IO() main = do -- On commence par ouvrir le fichier SAC en mode binaire argsList <- getArgs if (null argsList) then putStrLn $ "No filename given to the program.\n $ ProgramName file.sac" else do sacFile1 <- openBinaryFile (head argsList) ReadMode
position <- hTell sacFile1 putStrLn $ "Position 1: " ++ [intToDigit( fromInteger (position) )]
hSeek sacFile1 AbsoluteSeek 440 position2 <- hTell sacFile1 putStrLn $ "Position 2: " ++ [intToDigit( fromInteger (position2) )]
I don't think that's what you really want: Prelude Data.Char> intToDigit 440 *** Exception: Char.intToDigit: not a digit 440 perhaps you wanted putStrLn $ "Position 2: " ++ show position2 ?
-- A la fin, il faut evidemment le fermer hClose sacFile1
Thank you, Danke, 谢谢, merci, etc...