I'll work on putting the modules in that form while I try to track
down some info on how to re-write for late binding (all of my searches
so far have turned up results like "Hey! Did you know lisps have late
binding?" or "Late binding is important for making methods at
run-time." or "Plz read this CommonLisp-Scheme/Scheme-Scheme USENET
flamewar")

Felix

On Tue, Jan 26, 2021 at 4:22 AM Marc Nieper-Wißkirchen
<xxxxxx@nieper-wisskirchen.de> wrote:
>
> In what follows, I am only talking about R7RS, not about earlier Scheme standards, nor generally about implementation-specific stuff.
>
> In R7RS, we have to distinguish between two forms of `cond-expand`. The first form is an expression (described in 4.2.1. of the R7RS), the second form is a library declaration (described in 5.6.1. of the R7RS). Both forms have the same surface syntax and similar semantics.
>
> By the R7RS, the syntax of a library definition forces it to begin with `define-library`, so one cannot start a library definition with `cond-expand`, but one can portably use the library declaration form of `cond-expand`, just inside the `define-library` form. On the other hand, R7RS does not specify how library definitions are found by the system when an import is requested. A particular implementation may look for library definitions in implementation-specific `cond-expand` forms in implementation-specific places.
>
> In an R7RS top-level program, only the expression form of `cond-expand` is allowed. However, it is not available unless imported from `(scheme base)`. So, apart from the fact that an R7RS program has to start with an `import` form anyway, without one, there is no `cond-expand` anyway. As the import declarations in an R7RS top-level program all have to be at the beginning and may not be interspersed with definitions or expressions, one cannot use the `cond-expand` expression to guard imports in top-level programs.
>
> If you need to do the latter, you have to write a helper library, which is imported by your R7RS top-level program unconditionally, but which itself imports the actual libraries used conditionally through a `cond-expand` library declarations.
>
> Marc
>
> Am Di., 26. Jan. 2021 um 08:36 Uhr schrieb Felix Thibault <xxxxxx@gmail.com>:
>>
>> Looking at R7RS, I see that a library is supposed to start with a
>> define-library statement and a program is supposed to start with an
>> import statement. Both the main srfi/204.sld library and the
>> test/match-test.scm, which cover implementation and testing for Chibi,
>> Gauche, Guile, and Larceny, consist of a large cond-expand with a
>> block for each implementation (I've seen this style before in, say
>> srfi-64/testing.scm).
>>
>> Even though the standard and practice seemed to be in conflict, it was
>> not something I was aware of until I tried to integrate Unsyntax into
>> these files. Is this an error or a known issue or what? It seems like
>> it would reduce the usefulness of cond-expand if it couldn't be at the
>> top, but that's not what the spec says unless I am missing something.
>>
>> Felix