[Haskell-cafe] Parsec (Zero or One of)
Paul Keir
pkeir at dcs.gla.ac.uk
Tue Mar 25 11:31:19 EDT 2008
Hi,
I'm having some difficulty using the Parsec library, perhaps you could
help. I've reduced my problem as shown below. I would like the
'only_prod' parser to require the reserved string "only", _optionally_
followed by an identifier. As part of 'mytest', this should then be
followed by the reserved string "end".
mytest = do { only_prod; end }
only_prod = do { reserved "only"; try identifier }
end = reserved "end"
i.e. I'd like both
> parseTest mytest "only end"
and
>parseTest mytest "only green end"
to parse successfully. As it stands, only the second is successful. The
first fails with:
parse error at (line 1, column 9):
unexpected end of input
expecting letter or digit or "end"
Does anyone have an idea how I could repair the situation?
Thanks in advance,
Paul
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