[Haskell-cafe] Seeking a small bug-fix for previously-posted code

Stefan Holdermans stefan at cs.uu.nl
Sun Aug 14 06:05:00 EDT 2005


Just a quick hack:

   module Main where

   import List             -- ADDED
   import Graphics.UI.GLUT -- ADDED

   readVecs :: String -> IO [Vector3 GLfloat]
   readVecs f =
      do str <- readFile f
         -- FIXED LAYOUT:
         let mkVec [x,y,z] = Vector3 x y z
         let format line = "[" ++ concat (intersperse "," (words line)) 
++ "]"
           -- ADDED
         return $ map (mkVec . read . format)  $ lines str -- CORRECTED

So, the error message you got was layout-related, i.e., you needed to 
move the last two lines of you programs two positions to the left. 
Furthermore, you had to import the HOpenGL modules. Even then, your 
code did not type check, so I replaced the application of words in the 
last line by an application to a user-defined function format, that not 
even makes it type check but also makes it actually reformat the input 
so it can be consumed by read. I used intersperse to do this, so I also 
needed to import the List module.

But, seriously, do you really think this is the way to learn Haskell?

> And just one last question - If the file looked like this (with column 
> headings )
> Name  Ethnicity  Age
> Mary_Smith  NZ_European  27
> Joe_Brown    NZ_European  34
> John_Watson  Canadian  45
> Mike_Tangaroa  NZ_Maori  38
> - what change would the above code need to run?

I hope you don't mind I leave this to you as an exercise.



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