Am Mi., 24. Juni 2020 um 05:37 Uhr schrieb Alex Shinn <xxxxxx@gmail.com>:
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> On Fri, Jun 19, 2020 at 10:45 PM Marc Nieper-Wißkirchen <xxxxxx@nieper-wisskirchen.de> wrote:
>>
>> It would be an error if `displayed` is given a procedure, which is not a formatter.
>>
>> There's not much else we can do unless we make formatters a distinct type. This would need a new version of SRFI 165. And it will slow down the code because the record types encapsulating a formatter will have to be unpacked first.
>
>
> I don't think non-procedure formatters are likely, but it's best to allow for them.
>
> But we want to encourage portable code, which basically implies passing a non-formatter procedure *must* be an error, since in general implementations won't be able to distinguish which procedures are and aren't formatters.

Indeed.