On 2 Sep 2026, at 14:16, Andrew Tropin <xxxxxx@trop.in> wrote:

>> But this doesn’t answer the problem that the recommendation which seems to justify the existence of ‘set-current-test-runner!’ is ill advised. To clarify: if I import multiple libraries that provide test runners (because, for example, I want to make it a run time option to my test suite which is used), and each of them calls set-current-test-runner! to establish its own runner as the default, then under Scheme’s semantics it is unspecified which of those calls to set-current-test-runner! will run last and thus ‘win’, or indeed whether any of the calls at all will run.
>
> It's very unlikely case that multiple testing libraries will be loaded
> at the same time and if so, it's a responsibility of the user to set a
> proper default test runner.  I believe they will figure out how to setup
> their REPL environment for this case.

Sorry, I think I wasn’t clear enough about what the problem is here and only confused the issue by mentioning importing multiple test runners.

If a program (in the sense of the R6RS or R7RS small) to run a test suite looks like this:

(import (srfi :269)
        (rot13)
        (spiffing-test-runner))
(test "example library test" ()
  (is (string=? (string-rot13 "er") "re")))

And the (spiffing-test-runner) library looks like this:

(library (spiffing-test-runner)
  (export run-tests-spiffingly)
  (import (srfi :269)
          (rnrs)
          #;etc)
  (define (run-tests-spiffingly arg)
    #| code defines the test runner |#)
  (set-default-test-runner! run-tests-spiffingly))

Then it is unspecified whether the test will run with the run-tests-spiffingly procedure or with no test runner at all (unexpectedly triggering the ‘should produce a diagnostic indicating that no runner has been configured’). Because it is not lexically apparent to the compiler that the program actually depends on any identifiers from the (spiffing-test-runner) library, because none of its exported identifiers, the compiler may decide never to instantiate the library and thus may never run the set-default-test-runner! call. This is what I mean about the ‘may call set-default-test-runner! upon loading so that end users need not configure it manually’ recommendation being ill advised.

(Note that not all Scheme implementations have REPLs. A SRFI intended to be generally useful to Schemers of all stripes should be designed with a static ahead-of-time compiler in mind, as well as a highly interactive implementation like Guile.)

> This implemementation looks uglier, but seems to work.

This implementation will fail on static ahead-of-time compilers if there *aren’t* local bindings called ‘quote’ and ‘metadata’, because it will still insert a free reference to identifiers with those names into the expansion. It will be in dead code, but it will still be there.

Again, please just use a regular auxiliary syntax keyword and forget the ‘quote’. You can’t do what you’re trying to do in syntax-rules, because this is not how the syntax of Scheme is intended to work.

Daphne