On 10/12/09, Brandon S. Allbery KF8NH
On Oct 12, 2009, at 22:28 , Uwe Hollerbach wrote:
parsePrefixOf n str = string (take n str) >> opts (drop n str) >> return str where opts [] = return () opts (c:cs) = optional (char c >> opts cs)
Seems to me this will succeed as soon as it possibly can...
myTest = myPrefixOf 1 "banana" <|> myPrefixOf 1 "chocolate" <|> TPCP.try (myPrefixOf 2 "frito") <|> myPrefixOf 3 "fromage"
...so the "frito" branch gets committed as soon as "fr" is read/parsed (myTest returns)...
% ./opry fro "test" (line 1, column 3): unexpected "o" expecting "i", white space or end of input
...which is why this is looking for "white space or end of input".
My fix would be to have myPrefixOf require the prefix be terminated in whatever way is appropriate (end of input, white space, operator?) instead of simply accepting as soon as it gets a prefix match regardless of what follows.
-- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH
Ah, yes, I see where I went wrong; thank you! Uwe