Goedemiddag café,
Consider the following function, using parsec-3.0.0:
la :: Parsec String () (Maybe Char)
la = lookAhead (optionMaybe anyChar)
*Lookahead> parseTest (char 'a' <|> char 'b') "a"
'a'
*Lookahead> parseTest (char 'a' <|> char 'b') "b"
'b'
*Lookahead> parseTest (la *> char 'a' <|> char 'b') "a"
'a'
*Lookahead> parseTest (la *> char 'a' <|> char 'b') "b"
parse error at (line 1, column 2):
unexpected "b"
expecting "a"
The first three work fine and as expected, but the fourth example fails
where I would expect success. I know <|> won't try the rhs if the lhs
consumed input, but lookAhead's documentation promises not to consume
any input. Is this a bug in Parsec or am I missing something?
Thanks,
Martijn.
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