In R7RS, it is "an error" if one tried to parameterize a non-parameter
object. Since the only standard way is to make them using
"make-parameter," it would make sense to have a predicate on them to
check that you are not invoking an-error behavior. (If an implementation
checks that you are actually parameterizing a parameter object and
raises an exception if you pass the wrong value, then it has to have
some way of discriminating anyways. This would expose the mechanism used
to error check.)

A mechanism equivalent to SRFI 229/259 is in CHICKEN, Chez, Gauche,
Chibi, TR7, MIT-Scheme, Foment, and probably many others. Adding a
"parameter?" tag to a procedure made by "make-parameter" is pretty easy
in those implementations.

-- Peter McGoron

On 9/16/26 04:16, Marc Nieper-Wißkirchen wrote:
> - I don't get the "need" for `parameter?`.  What is this supposed to
> mean when parameters can be procedures?