Hi,
1. your "lookAhead" is unnecessary, because your items (atomNames) never
start with "%".
2. your "try" fails in (line 12, column 1), because the last item (aka
atomName) starts consuming "\n", before your eol parser is called.
So rather than calling spaces before every real atom, I would call it
after every real atom and after your formatDecl (so before your linesOf
parser).
atomNameBlock = do flagDecl "ATOM_NAME"
formatDecl
spaces
atomNames <- many1 atomName
return $ AtomNames atomNames
where
atomName = do
name <- countBetween 1 4 (alphaNum <|>
oneOf "\'+-") <?> "atom name"
spaces
return name
Since spaces also consume "\n", linesOf can just be "many1"!
HTH Christian
Am 21.09.2011 05:32, schrieb Ben Gamari:
Recently I've been playing around with Parsec for a simple parsing
project. While I was able to quickly construct my grammar (simplified
version attached), getting it working has been a bit tricky. In
particular, I am now stuck trying to figure out why Parsec is
mis-reporting line numbers. Parsec seems convinced that line 12 of my
input (also attached) has a "%" character,
$ runghc Test.hs
Left "(unknown)" (line 12, column 1):
unexpected "%"
expecting space or atom name
while my file clearly disagrees,
10 %FLAG ATOM_NAME
11 %FORMAT(20a4)
12 C1 H1 C2 H2 C3 H3 C4 H4 C5 C6 C7 C8 N1 C9 H9 C10 H10 C11
H11 C12
13 H12 C13 H13 C14 C15 N2 C16 C17 C29 H18 C19 H19 C20 H20 C21 H21 C22
H221H222H223
...
18 %FLAG CHARGE
19 %FORMAT(5E16.8)
The task here is to identify the block of data lines (lines 12-17),
ending at the beginning of the next block (starting with "%"). It seems
likely that my problem stems from the fact that I use "try" to
accomplish this but this is as far as I can reason.
Any ideas what might cause this sort of off-by-one? Does anyone see a
better (i.e. working) way to formulate my grammar? Any and all help
would be greatly appreciated. Thanks.
Cheers,
- Ben
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