Relatedly, R6RS is clear that an identifier matches a literal in a syntax-case clause iff they're free-identifier=?, but as far as I can see, it does not clarify how the literals themselves in the syntax-case clause are recognized, namely what predicate is used to match them against the literals list of the syntax-case expression.
Test program:
(define-syntax build-syntax
(syntax-rules ()
((_ expr expr* ...)
(let-syntax ((temp-macro (lambda (ignored-syntax)
expr expr* ...)))
(temp-macro)))))
(build-syntax
(with-syntax ((foo1 (let ((foo 'foo)) #'foo))
(foo2 (let ((foo 'foo)) #'foo)))
(with-syntax ((foo1-foo2-free=? (free-identifier=? #'foo1 #'foo2))
(foo1-foo2-bound=? (bound-identifier=? #'foo1 #'foo2)))
(syntax
(begin
(display "free-identifier=? ")
(display foo1-foo2-free=?)
(newline)
(display "bound-identifier=? ")
(display foo1-foo2-bound=?)
(newline)
(syntax-case #'not-foo (foo1)
(foo2
(display "Matched as literal\n"))
(_
(display "Not matched\n"))))))))
Guile 3.0:
free-identifier=? #f
bound-identifier=? #t
Matched as literal
Racket:
free-identifier=? #t
bound-identifier=? #t
Not matched
As you can see, foo1 and foo2 are *more* equal in Racket (also free-identifier=?
in addition to being bound-identifier=?), yet they don't match in Racket whereas
they do in Guile.
Chez Scheme gives the same identifier predicate results as Guile,
but it doesn't consider them matched:
free-identifier=? #f
bound-identifier=? #t
Not matched
Kawa somehow doesn't even handle the program:
free-identifier=? #t
bound-identifier=? #t
java.lang.NullPointerException: Cannot invoke
"kawa.lang.Translator.getCurrentSyntax()" because "tr" is null
at kawa.lang.SyntaxPattern.match(SyntaxPattern.java:604)
at kawa.lang.SyntaxPattern.match(SyntaxPattern.java:88)
at tmp2.run(tmp2.scm:6)
at gnu.expr.ModuleExp.evalModule2(ModuleExp.java:290)
at gnu.expr.CompiledModule.evalModule(CompiledModule.java:42)
at gnu.expr.CompiledModule.evalModule(CompiledModule.java:60)
at kawa.Shell.runFile(Shell.java:571)
at kawa.Shell.runFileOrClass(Shell.java:474)
at kawa.repl.processArgs(repl.java:710)
at kawa.repl.main(repl.java:830)
free-identifier=? #f
bound-identifier=? #t
Not matched
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