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
)
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