[Scm-discuss] unquote-splicing problem in macro expansion

[Richard Russo]

I'm experiencing a problem with unquote-splicing while an outer macro 
expansion is being evaluated. Here are minimal steps to reproduce the 
problem:

-----------------------------
D:\temp\scm>scm -r5
> (define-syntax a-macro (syntax-rules () ((_ (arg ...) body ...) 
(lambda (arg ...) body ...))))
#<unspecified>
> (a-macro () `(foo ,@(list 1 2 3)))

;ERROR: unquote-splicing invalid-context-within-quasiquote
>
-----------------------------

I've been able to reproduce this problem using several builds of scm for 
windows: 5e5-1, 5e6-1, 5e7-1, 5f1-1. On my Debian system with the 5e5-1 
scm package installed, the problem does not reproduce. This error is 
reported by the slib function hyg:untag-quasiquote in mbe.scm. I did not 
notice any difference in the slib builds corresponding to the different 
scm builds I tested. My current assumption is the problem lies in the 
windows build of scm.

I did take a look at the 5f-1 scm source, scanning instances of _WIN32, 
__WINDOWS__ and looking through some of the macro expansion code in 
eval.c. So far I'm coming up short as to the root cause of the problem.

Has anyone else experienced this issue or have a suggestion as to what 
the root cause might be?

- Richard

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