Several times now, I've run into one or another form of the following
problem:
Say I want to build primitives to
1. declare an "interface" as a list of names, and
2. implement and use those names at run time in a limited scope
Concretely, I want to run the following code:
(interface Speaker say speak)
(implement Speaker displayln (say 'hello) speak)
If I put these lines at the end of a file that implements the two forms, it
should (displayln 'hello) when I run it.
Here is the interface macro:
(define-syntax (interface stx)
(syntax-case stx ()
[(_ id member-id ...) #'(define-syntax id #'(member-id ...))]))
The implement macro is trickier. A naive implementation looks like this:
(define-syntax (implement stx)
(syntax-case stx ()
[(_ class-id def ... expr)
(with-syntax ([(id ...) (syntax-e (syntax-local-value #'class-id))])
#'(letrec ([id def] ...) expr))]))
It fails with the following message:
; /tmp/j.rkt:44:30: say: unbound identifier; in: say; context...:;
#(570423 use-site) [common scopes]; other binding...:; local;
#(570422 macro) [common scopes]; common scopes...:; #(570223
module) #(570226 module j) #(570426 local) #(570427 intdef);
#(570428 local)
Incorporating the debug-scopes package's +scopes macro shows this:
(letrec⁰˙˙¹
((say⁰˙˙¹ displayln⁰˙˙³) (speak⁰˙˙¹ (say⁰˙˙³ (quote⁰˙˙³ hello⁰˙˙³))))
speak⁰˙˙³)ˢˡⁱ⁼²⁺ᵘˢᵉ⁼³0 module 5705121 module j 5705152 macro
5707193 use-site 570720
For reasons I don't yet fully comprehend, it just works out if I use
syntax-local-introduce on the id's, so +scopes gives me this:
(letrec⁰˙˙¹
((say⁰˙˙³ displayln⁰˙˙³) (speak⁰˙˙³ (say⁰˙˙³ (quote⁰˙˙³ hello⁰˙˙³))))
speak⁰˙˙³)ˢˡⁱ⁼²⁺ᵘˢᵉ⁼³0 module 5712471 module j 5712502 macro
5714553 use-site 571456
But if the interface and implement invocations are not in the same file as
their implementations, it breaks with a similar error:
; /tmp/h.rkt:5:30: say: unbound identifier; in: say; context...:;
#(572682 module) [common scopes]; other binding...:; local;
#(572388 module) #(572391 module j) #(572596 module); #(572599
module j) [common scopes]; common scopes...:; #(572685 module h)
#(572700 local) #(572701 intdef) #(572702 local)
In this situation, +scopes gives:
(letrec⁰˙˙³
((say⁴˙˙⁵ displayln⁴˙˙⁶) (speak⁴˙˙⁵ (say⁴˙˙⁶ (quote⁴˙˙⁶ hello⁴˙˙⁶))))
speak⁴˙˙⁶)ˢˡⁱ⁼⁶⁺ᵘˢᵉ⁼0 module 5768541 module j 5768572 module
5770563 module j 5770594 module 5771505 module h 5771536 macro
577173
If I move the interface invocation back into the original file and keep the
implement invocation in a separate file, I get the same error but +scopes
gives something slightly different:
(letrec⁰˙˙³
((say⁰˙˙⁴ displayln⁴˙˙⁶) (speak⁰˙˙⁴ (say⁴˙˙⁶ (quote⁴˙˙⁶ hello⁴˙˙⁶))))
speak⁴˙˙⁶)ˢˡⁱ⁼⁴⁺ᵘˢᵉ⁼0 module 5723881 module j 5723912 module
5725963 module j 5725994 macro 5726975 module 5726826 module h
572685
What's going on here? How do I fix this?
Eric
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