[Haskell-beginners] Parse error in pattern

[Florian Duret]

Hello,


I try to set up a verification on the number of arguments given to my
program, but keep on getting "Parse error in pattern"

Here is what my code looks like:

main :: IO()
main = do
    -- On commence par ouvrir le fichier SAC en mode binaire
    argsList <- getArgs
    if (length (argsList) == 0)
       then do
             putStrLn $ "No filename given to the program.\n $ ProgramName
file.sac"
             return ()
      else
             sacFile1 <- openBinaryFile fileToOpen ReadMode

ghci complains, and tells "Parse error in pattern", indicating the 'if' line
number.

Can you please help ?
Thank you very much,
Florian
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