[Haskell-cafe] How is this variable not in scope?

[Alejandro Serrano Mena]

The problem is that in the "where" clause the only things which are in
scope are (roughly) the arguments of the function. In particular, neither
"root" nor "inputFile" nor "input" nor "pairs". The solution is to add an
extra argument:

main' = do
  ...
  mapM_ (f root) pairs where
    f root (name, content) = writeFile (root ++ name) content

2017-07-21 9:28 GMT+02:00 Jeffrey Brown <jeffbrown.the at gmail.com>:

> The following compiles and runs perfectly:
>
> main = do
>   (inputFile:_)  <- getArgs
>   input <- readFile inputFile
>   let pairs = pairFilesToContents $ readSmsnLines input
>   mapM_ f pairs where
>     f :: (FilePath, String) -> IO ()
>     f (name, content) = writeFile name content
>
> But the following triggers the error "Not in scope: ‘root’".
>
> main' = do
>   (root : inputFile :_)  <- getArgs
>   input <- readFile inputFile
>   let pairs = pairFilesToContents $ readSmsnLines input
>   mapM_ f pairs where
>     f :: (FilePath, String) -> IO ()
>     f (name, content) = writeFile (root+name) content
>
> --
> Jeff Brown | Jeffrey Benjamin Brown
> Website <https://msu.edu/~brown202/>   |   Facebook
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>
>
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