[Haskell-cafe] handling read exceptions
Sven.Panne at aedion.de
Tue Apr 13 09:54:35 EDT 2004
S. Alexander Jacobson wrote:
> My point is that I am reading in name/value pairs
> and once I know the name, I know the type of the
> value, but I don't want to have to pass that
> information programatically to the point in the
> code where I am doing the read.
OK, I see... I don't know the exact syntax you are using (e.g. how
are the strings terminated?), but "reads" is still useful:
readIS :: ReadS (Either Integer String)
readIS s = take 1 $
[ (Left x, t) | (x, t) <- reads s ] ++
[ (Right x, t) | (x, t) <- lex s ]
Then we have:
Main> readIS "123blah"
Main> readIS "blah123"
Main> readIS ""
Main> readIS "foo bar"
[(Right "foo"," bar")]
If you have only simple parsing tasks and are not looking for extreme
performance, the Read class is a good choice. Otherwise you should
probably have a look at the Parsec package which comes with Hugs and GHC:
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