I have a macro that creates transformer bindings at phases 0 and 1:
(define-syntax (f stx)
(with-syntax ([name (cadr (syntax-e stx))])
#'(begin
(define-syntax name (syntax-id-rules () [_ 1]))
(begin-for-syntax (define-syntax name (syntax-id-rules () [_
2]))))))
Normally, this works fine. I have syntax transformers bound at both phases
that can resolve "name" with syntax-local-value.
In an expression context, the phase-0 transformer binding can be
overridden temporarily with let-syntax:
(cons
x (let-syntax
([x (syntax-id-rules () [_ 'one])]
[y (λ (stx) (datum->syntax stx (syntax-local-value #'x)))])
(list x y)))
This produces '(1 one #<set!-transformer>). With syntax-local-eval instead
of syntax-local-value, it produces '(1 one 2).
Because "f" produces begin-for-syntax, it only works in a module or
top-level evaluation context:
(let () (f x) x)
/tmp/g.rkt:10:8: begin-for-syntax: not in a definition context
in: (begin-for-syntax (define-syntax x (syntax-id-rules () (_ 2))))
Is there a way to override temporarily the phase-1 transformer binding as
well?
Eric
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