On 2020-03-10 9:35 a.m., John Cowan wrote:

What happens with an invalid argument to make-codec?

As is usual with domain errors in Scheme, "it is an error", which means the implementation can do whatever it wants, just as it can with (car 1). Some possibilities might be to signal an error, to return #f or some other random value, to crash the program, or to make demons fly out of your nose.  See <http://catb.org/jargon/html/N/nasal-demons.html>.

It didn't say “it is an error”, so that should be stated explicitly. This is one of those cases where I'd strongly prefer the statement to be “an error is raised”, as (a) make-codec will know that it didn't  find the specified string (unlike (car 1), especially in compiled code with safeties off), and (b) there's a potential of creating a codec that transcodes into Old Glagolitic and then writing out reams of drivel when the user thought that the implementation supported Modern Klingon.

So +1 for “an error is raised”. -- vincent