[Haskell-cafe] Unifcation and matching in Abelian groups

[Neil Mitchell]

Hi,

I ran your code thought HLint
(http://community.haskell.org/~ndm/hlint), and it suggested a couple
of things (mainly eta reduce). The most interesting suggestions are on
your main function:

> main :: IO ()
> main =
>     do
>       done <- isEOF
>       case done of
>         True -> return ()
>         False ->
>             do
>               prob <- getLine
>               test prob
>               main

It suggests:

Example.lhs:432:3: Warning: Use if
Found:
  case done of
      True -> return ()
      False -> do prob <- getLine
                  test prob
                  main
Why not:
  if done then return () else
    do prob <- getLine
       test prob
       main

Changing that and rerunning says:

Example.lhs:432:3: Error: Use unless
Found:
  if done then return () else
    do prob <- getLine
       test prob
       main
Why not:
  unless done $
    do prob <- getLine
       test prob
       main

So I (or rather HLint) recommends you do:

> main :: IO ()
> main =
>     do
>       done <- isEOF
>       unless done $ do
>               prob <- getLine
>               test prob
>               main

Thanks, Neil