It works when I change my mag-line syntax class to:
(define-syntax-class mag-line
(pattern (line expr ...)))
So removing the literal specifier on line seems to work. I'm still not sure
why the two modules behave differently though. It seemed to work in
expander-utils.rkt whether line was defined or not. So there must be
something in the compilation environment that I'm missing. I'm still
curious if anyone has a good explanation. I may hit issues with level
further down the road as well.
-- Jonathan
On Saturday, September 28, 2019 at 6:30:54 PM UTC-4, Jonathan Simpson wrote:
>
> I've recently been rewriting some ugly code to make it fully hygienic with
> syntax-parse. I have an implementation that appears to work when testing it
> from the module that contains the macros, but it fails when I run it from
> my main program/another module.
>
> The macro in question is parse-level0, defined in expander-utils.rkt:
>
> ----
> (begin-for-syntax
> (define-syntax-class mag-lvl
> (pattern ({~datum level})))
>
> (define-syntax-class mag-line
> (pattern ({~literal line} expr ...))))
>
> (define-syntax (parse-level0 stx)
> (printf "parse-level0 input: ")
> (display stx) (printf "~n")
> (syntax-parse stx
> [(_ ln:mag-line) #'ln]
> [(_ ln:mag-line (~seq lvl:mag-lvl ...+ ln2:mag-line) ...+)
> #:with branch-lines #'((~@ lvl ... ln2) ...)
> (printf "parse-level0 1~n")
> #`(when* ln (level
> #,@(parse-level1 #'branch-lines)))]
> [(_ lvl:mag-lvl ...+ expr ...)
> #'(error "no line at level 0")]
> [_
> (printf "parse-level0 error on input: ")
> (display stx) (printf "~n")
> #'(error "syntax error at level 0")]))
> ----
>
> This macro is provided to expander.rkt. It works when run from the REPL in
> expander-utils.rkt, but not when run from expander.rkt. Here's an example
> with some debug info printed:
>
> expander-utils.rkt> (parse-level0 (line 1))
> parse-level0 input: #<syntax:stdin::10915 (parse-level0 (line 1))>
> '(1)
> expander-utils.rkt>
> expander.rkt> (parse-level0 (line 1))
> parse-level0 input: #<syntax:stdin::11004 (parse-level0 (line 1))>
> parse-level0 error on input: #<syntax:stdin::11004 (parse-level0 (line 1))>
> ; syntax error at level 0
> ; Context:
> ; /usr/local/racket/collects/racket/repl.rkt:11:26
>
> The syntax objects there are printed with 'display' and are identical as
> far as I can tell, but I wonder if it could be related to interpreting line
> or level as a datum or literal as defined in the syntax classes I created.
> In this example I'm not using level so I guess that it wouldn't matter, but
> line is defined as a macro in expander.rkt. But it still works in
> expander-utils.rkt if I define the line macro there.
>
> Anyone have an idea what might be happening here?
>
> Full code available at https://github.com/jjsimpso/magic.
>
> Thanks,
> Jonathan
>
>
>
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