I think there are two issues here:
1. The stack trace in your email is just a result of `raco make`
printing its current context when there's a syntax error. If you
replace the whole body of the module with just `(lambda)`, you'll see
the same stack trace. Probably `raco make` should be changed not to
print that part of the stack.
2. `(require (for-syntax racket/function))` would be needed if you
used `thunk` to compute the new syntax that your macro expanded into
-- in other words, if `thunk` gets executed during expansion. However,
your macro expands into a use of `thunk`, just like it expands into a
use of `reify-thunk`. If we rewrite your macro not using
`syntax-rules, the distinction is perhaps clearer:
(define-syntax reify (lambda (stx) (syntax-case stx () [(_ e)
(syntax (reify-thunk (thunk e)))])))
The things used in the computation of the new syntax are, here,
`lambda`, `syntax-case`, and `syntax`. `reify-thunk` and `thunk`
appear inside `syntax` -- they are part of the program that we expand
into, and thus need to be available at phase 0.
Hopefully that helps explain what's going on here.
Sam
On Tue, Oct 6, 2015 at 7:18 PM, Paolo Giarrusso <p.giarru...@gmail.com> wrote:
> I feel I've found (and minimized) a perfectly repeatable bug in separate
> compilation in Racket 6.2.1, or at least a situation which is a pain to debug
> for related reasons. The example code is available at
> http://pasterack.org/pastes/25050 (or at the end of this email) with all
> modules in one file, but I've first obtained it with modules in separate
> files.
>
> In module base-sig, I can use an identifier (here `thunk`) which is *not* in
> scope in a "macro" (?) inside define-signature. In module base (which
> requires module base-sig) I provide a unit implementing the signature. Then,
> if in module client I require module base, load the unit *and use the macro*,
> I get a compiler stacktrace mentioning `thunk`, even though `thunk` isn't
> mentioned (except after macro expansion). No error before.
> To fix this, I must trace this to module 1 by trial and error — requires
> elsewhere won't help (because lexical scope is still respected).
>
> The needed fix is not (require (for-syntax) but a plain (require). That seems
> to be as specified, but it seems unintuitive wrt. the phase distinction — I
> can imagine this makes sense for units, but it should IMHO be better
> explained. More importantly, undeclared identifiers should be flagged early.
>
>> Each define-syntaxes form in a signature declaration introduces a macro that
>> is available for use in any unit that imports the signature. Free variables
>> in the definition’s expr refer to other identifiers in the signature first,
>> or the context of the define-signature form if the signature does not
>> include the identifier.
>
> $ raco make all.rkt
> all.rkt:11:24: thunk: unbound identifier in module
> in: thunk
> compilation context...:
>
> /Users/pgiarrusso/AeroFS/Repos/racket-playground-bluevelvet/bug-with-signatures-and-macros/all.rkt
> context...:
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:341:0: compile-zo*
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:556:26
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:548:42
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:513:0:
> maybe-compile-zo
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:628:2: do-check
> /Users/pgiarrusso/opt/racket/collects/compiler/cm.rkt:708:4
>
> /Users/pgiarrusso/opt/racket/share/pkgs/compiler-lib/compiler/commands/make.rkt:81:8:
> for-loop
>
> /Users/pgiarrusso/opt/racket/share/pkgs/compiler-lib/compiler/commands/make.rkt:
> [running body]
> /Users/pgiarrusso/opt/racket/collects/raco/raco.rkt: [running body]
> /Users/pgiarrusso/opt/racket/collects/raco/main.rkt: [running body]
>
> ==
>
> #lang racket
> (module base-sig racket/base
> (require racket/unit)
> (require (only-in racket/function thunk)) ; Omitting this line crashes the
> compiler
>
> (define-signature reify^
> (reify-thunk
> (define-syntaxes (reify)
> (syntax-rules ()
> [(_ e)
> (reify-thunk (thunk e))]))
> ))
>
> (provide reify^))
>
> (module base racket/base
> (require racket/unit)
> (require racket/control)
> (require (submod ".." base-sig))
>
> (define-unit reify@
> (import)
> (export reify^)
> (define (reify-thunk computation)
> (reset (computation)))
> )
> (provide reify@))
>
> (module client racket
> (require (submod ".." base))
> (define-values/invoke-unit/infer reify@)
>
> (reify 0) ; This call is needed to trigger the crash
> )
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google Groups
"Racket Users" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to racket-users+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/d/optout.
