Re: [Jscheme-user] a little problem with define-macro

[Timothy J. H. <tim...@ma...>]

On Apr 7, 2004, at 12:27 AM, Borislav Iordanov wrote:

> Hi,
>
> I tried using define-macro (i.e. the built in macros) to simplify
> working with streams thus:
>
>> (define-macro (make-stream h t) (cons h (delay t)))
> (macro make-stream (h t)...)

The define-macro should return an s-expression which will
then be evaluated:

     (define-macro (make-stream h t) `(cons ,h (delay ,t)))

This works fine with enum. The quasiquoted expression
could also be written with standard quote as

   (define-macro (make-stream h t) (list 'cons h (list 'delay t)))

which would work as well, but is harder to read...

---Tim---


>
> But then:
>
>> (define (enum start end)
>    (if (> start end) '() (make-stream start (enum (+ start 1) end))))
>
> SchemeException: expected object of type list (i.e. pair or empty), but
> got: , "
> (lambda delay~3 ()...)"
>         at jsint.E.error(E.java:14)
>         at jsint.E.typeError(E.java:24)
>         at jsint.U.toList(U.java:180)
>         at jsint.U.listToVector(U.java:772)
>         at jsint.Scheme.analyze(Scheme.java:487)
>         at jsint.Scheme.analyze(Scheme.java:475)
>         at jsint.Scheme.analyze(Scheme.java:490)
>         at jsint.Scheme.analyze(Scheme.java:473)
>         at jsint.Scheme.analyze(Scheme.java:459)
>         at jsint.Scheme.analyze(Scheme.java:490)
>         at jsint.Scheme.analyze(Scheme.java:490)
>         at jsint.Scheme.analyze(Scheme.java:475)
>         at jsint.Scheme.eval(Scheme.java:434)
>         at jsint.Scheme.eval(Scheme.java:424)
>         at jsint.Scheme.readEvalWriteLoop(Scheme.java:208)
>         at jsint.Scheme.runJscheme(Scheme.java:186)
>         at jsint.Scheme.defaultMain(Scheme.java:149)
>         at jsint.Scheme.main(Scheme.java:124)
>         at jscheme.REPL.main(REPL.java:138)
>
>
> If expand "manually" the macro:
>
> (define (enum start end)
>    (if (> start end) '() (cons start (delay (enum (+ start 1) end)))))
>
> there is no problem.
>
> BTW, it also works with define-syntax macros..
>
> Best,
> Boris
>
>
>
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