[Haskell-cafe] Re: [Haskell] Going nuts

[Albert Lai]

"Alexandre Weffort Thenorio" <alethenorio at home.se> writes:

> outputLine keyno key orgFile = do
>     part1 <- getLeft keyno orgFile
>     part2 <- getRight keyno orgFile
>     total <- part1 ++ (strUpper key) ++ part2 ++ "\n"
>     newHexFile <- openFileEx "newfile" (BinaryMode WriteMode)
>      hPutStrLn newHexFile (orgFile!!0 ++ "\n" ++ total ++ unlines (drop 2
> orgFile))

outputLine keyno key orgFile = do
    let part1 = getLeft keyno orgFile
    let part2 = getRight keyno orgFile
    let total = part1 ++ (strUpper key) ++ part2 ++ "\n"
    newHexFile <- openFileEx "newfile" (BinaryMode WriteMode)
    hPutStrLn newHexFile (orgFile!!0 ++ "\n" ++ total ++ unlines (drop 2 orgFile))

"let ... =" instead of "<-" because getLeft et al. aren't IO commands.

(Why type error rather than syntax error then? Because getLeft returns
a list, and list is a monad too. E.g.,

  do { part1 <- getLeft keyno orgFile; return part1 }
= [ part1 | part1 <- getLeft keyno orgFile ]

so part1 is inferred to be a Char.)

There will be another problem.  The type of orgFile is expected to be
String here, but the callsite gives it "lines(hexFile)" of type [String].