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? Many thanks in advance! _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/
Am Montag, 9. Januar 2006 12:52 schrieb Gerd M:
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?
Many thanks in advance!
I'm almost convinced, you don't really want to parse a list of (SourcePos,Tok) pairs. The SourcePos is taken care of in the internal state of the parsers. And maybe, you should use tokenPrim instead of token. Then you'd probably get something like type MyParser a = GenParser Tok () a mytoken :: (Tok -> Maybe a) -> MyParser a mytoken test = tokenPrim show update test where update pos tok toks = case tok of NewL -> setSourceColumn (incSourceLine pos 1) 1 _ -> incSourceColumn pos 1 or whatever is an appropriate update function for the SourcePos. If Tok is Char, of course a wealth of parsers are already supplied. HTH Cheers, Daniel
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?
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?
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participants (3)
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Christian Maeder -
Daniel Fischer -
Gerd M