[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Am 29.09.2010 09:54, schrieb Christian Maeder: Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. if you want to match a final tag, you could try: manyTill tagOrContent (try (aTag eof)) Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) this also looks like manyTill anyChar tagEnd C. tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Am 29.09.2010 11:55, schrieb Christian Maeder: Am 29.09.2010 09:54, schrieb Christian Maeder: Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. if you want to match a final tag, you could try: manyTill tagOrContent (try (aTag eof)) better yet, avoiding backtracking, return different things for aTag and someContents and check if the last entry is a tag. tagOrContent = fmap Left aTag | fmap Right someContent taggedContent = do spaces aTag l - many tagOrContent eof case reverse l of Left _ : _ - return () _ - fail expected final tag before EOF C. Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) this also looks like manyTill anyChar tagEnd C. tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Antoine and Christian: Many thanks for your help on this thread. (I am still digesting it; much appreciated; will post when I get it working.) -- Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question
Michael Mossey wrote: Here's what I have so far. It works, but it's a bit weird to consume the // as part of the text rather than the keyword. That happens because the try( string // ), which is part of the end arg to manyTill, consumes the // when it succeeds. But maybe it is the most natural way to express the problem. use lookAhead! parseKeyword :: Parser String parseKeyword = many1 (alphaNum | char '_') parseKeyword = string // many1 (alphaNum | char '_') parseText :: Parser String parseText = manyTill anyChar ((try (string //) return ()) | eof) parseText = manyTill anyChar $ (lookAhead (try $ string //) return ()) | eof (untested) C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question
Erik de Castro Lopo schrieb: Erik de Castro Lopo wrote: qualifiedIdentifier :: CharParser st [ String ] Ahh, figured it out myself: qualifiedIdentifier :: CharParser st [ String ] qualifiedIdentifier = do i - identifier r - dotIdentifier return (i : r) where dotIdentifier = do char '.' i - identifier r - dotIdentifier return (i : r) | return [] Does that look sane to people who know Haskell and Parsec better than me? Hi Erik, have a look at the module Text.ParserCombinators.Parsec.Combinator. Those functions should help you to build up parsers from smaller building blocks. Using sepBy1, the above parser can be written as dot = T.dot lexer qualifiedIdentifier = sepBy1 identifier dot benedikt ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec question
Benedikt Huber wrote: have a look at the module Text.ParserCombinators.Parsec.Combinator. Those functions should help you to build up parsers from smaller building blocks. Using sepBy1, the above parser can be written as dot = T.dot lexer qualifiedIdentifier = sepBy1 identifier dot WOW That is really impressive! Thanks, Erik -- - Erik de Castro Lopo - One serious obstacle to the adoption of good programming languages is the notion that everything has to be sacrificed for speed. In computer languages as in life, speed kills. -- Mike Vanier ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec question
Benedikt Huber wrote:
Using sepBy1, the above parser can be written as
dot = T.dot lexer
qualifiedIdentifier = sepBy1 identifier dot
My next problem is matching things like:
identifier ('.' identifier)* ('.' '*')?
I've had a look at lookAhead from Text.ParserCombinators.Parsec.Combinator
but I can't get it to work.
Clues?
Erik
--
-
Erik de Castro Lopo
-
That being done, all you have to do next is call free() slightly
less often than malloc(). You may want to examine the Solaris
system libraries for a particularly ambitious implementation of
this technique.
-- Eric O'Dell (comp.lang.dylan)
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Re: [Haskell-cafe] Re: Parsec question
On Wed, Dec 24, 2008 at 9:22 AM, Erik de Castro Lopo
mle...@mega-nerd.com wrote:
My next problem is matching things like:
identifier ('.' identifier)* ('.' '*')?
I've had a look at lookAhead from Text.ParserCombinators.Parsec.Combinator
but I can't get it to work.
* is analogous to the 'many' combinator, and ? can be implemented with
the 'option' combinator. Parsec is all about composing bigger parsers
out of smaller ones using combinators like these.
One of the tricks I found early on is to understand where to use 'try'
(since by default input is consumed even if a parser fails) but apart
from that just read Daan's page, even though it's out of date, and
look at how all these cool combinators work.
http://legacy.cs.uu.nl/daan/download/parsec/parsec.html
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Re: [Haskell-cafe] Re: Parsec question
Toby Hutton wrote: One of the tricks I found early on is to understand where to use 'try' (since by default input is consumed even if a parser fails) but apart from that just read Daan's page, even though it's out of date, and look at how all these cool combinators work. http://legacy.cs.uu.nl/daan/download/parsec/parsec.html Ah yes, reading that document and using 'try' is a good tip. This is what I cam up with: qualifiedIdentStar :: CharParser st [ String ] qualifiedIdentStar = do try identDotStar | qualifiedIdentifier where identDotStar = do s - sepEndBy1 identifier dot char '*' return (s ++ [ * ]) Cheers, Erik -- - Erik de Castro Lopo - It has been discovered that C++ provides a remarkable facility for concealing the trival details of a program -- such as where its bugs are. -- David Keppel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec Question
Hi Gerd, despite SourcePos being abstract, it can be fully manipulated using newPos. import Text.ParserCombinators.Parsec.Pos If you can compute the positions from your Tok-stream then you may consider using tokenPrim and work with GenParser Tok () a HTH Christian Gerd M wrote: I'm trying to use parsec for parsing a custom input stream. As far as I understood the manual correctly I need to define the primitive parser: type MyParser a = GenParser (SourcePos,Tok) () a mytoken :: (Tok - Maybe a) - MyParser a mytoken test = token showToken posToken testToken where showToken (pos,tok) = show tok posToken (pos,tok) = pos testToken (pos,tok) = test tok The problem is, since SourcePos is an abstract datatype, how can I actually run this parser without explicitly using values of type SourcePos in the input stream? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec Question
despite SourcePos being abstract, it can be fully manipulated using newPos. Thanks for the tip, I thought it wasn't exported. Gerd M wrote: I'm trying to use parsec for parsing a custom input stream. As far as I understood the manual correctly I need to define the primitive parser: type MyParser a = GenParser (SourcePos,Tok) () a mytoken :: (Tok - Maybe a) - MyParser a mytoken test = token showToken posToken testToken where showToken (pos,tok) = show tok posToken (pos,tok) = pos testToken (pos,tok) = test tok The problem is, since SourcePos is an abstract datatype, how can I actually run this parser without explicitly using values of type SourcePos in the input stream? _ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
