Handling Errors (continued)

[Gustavo Villavicencio]

Before nothing, thanks Axel and Alastair.

Following your suggestions i have constructed another two
solutions:

1- getMem s = catch (do m <- newCString s
                        return m)
                    (\_ -> return nullPtr)
              -- the exception handler could be more elaborated.

2- fpred p | p == nullPtr = True
           | otherwise    = False

   getMem s = throwIf (fpred)
                      (\nullPtr -> "memory out")
                      (do m <- newCString s
                          return m)
in both cases

main = getMem s1 >>= \p1 ->
       getMem s2 >>= \p2 ->
       let p3 = hstrL p2 p1
       in peekCString p3 >>= \s ->
          print s

Which of the three solutions, including those of Alastair,
would be better?. Can one fail and other one not in
some situation?.
Thanks again for your help,
gustavo