[racket] lexer-src-pos reports position as #f #f

Did you not enable line counting with port-count-lines! as instructed
by the documentation:

"Since the lexer gets its source information from the port, use
port-count-lines! to enable the tracking of line and column
information. Otherwise, the line and column information will return
#f."

?

Jay

2011/5/24 Johnny Morrice <spoon at killersmurf.com>:
> Hi list,
>
> I'm trying to build a lexer with lexer-src-pos from parser-tools/lex.
>
> I've written some unit tests which use pipes to provide an input port
> to the lexer.
>
> My problem is that the lexer does not seem to report the correct
> line numbers.  Apparently, the line number is #f.
>
> I don't understand what I'm doing wrong.
>
> If I run this through racket v5.1.1:
>
> #lang racket
>
> (require parser-tools/lex)
>
> (define no-pos-lexer
>  (lexer-src-pos
>    [any-char lexeme]))
>
> (let-values ([(i o) (make-pipe)])
>            (display "$" o)
>            (let* ([no-pos-token (no-pos-lexer i)]
>                   [no-pos (position-token-start-pos no-pos-token)])
>              (printf "Token ~a at line ~a, column ~a\n"
>                      (position-token-token no-pos-token)
>                      (position-line no-pos)
>                      (position-col no-pos))))
>
> It outputs:
> Token $ at line #f, column #f
>
> But I would like it to output:
> Token $ at line 1, column 1
>
> Where am I going wrong?
>
> Thanks
> Johnny
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-- 
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://faculty.cs.byu.edu/~jay

"The glory of God is Intelligence" - D&C 93