In SRFI 173, the definition of hook-run says:

"The length of ARGS must be equal to the arity of the HOOK object."

But in writing Scheme standards (other than R6RS, which has different rules), the word "must" specifies what the implementation must do, rather than what the user must do. Not all SRFIs respect this, but most do.

On checking the implementation, SRFI 145 `assume` is used to check this constraint. I am proposing therefore that the wording be changed to:

"It is an error if the length of ARGS is not equal to the arity of the HOOK object."

I don't think this requires a post-finalization note.

Comments? If people are happy with this, there will be a bunch of similar messages for other SRFIs.