Instead of "expression-arity", I would suggest

"coarity" (as the dual to "arity")

 

identity - Yes, it is identity (in multiple-value sense), but we already have values.  The procedure "identity" is frequently defined

   as one-argument, one-value procedure and at least Gauche adopted it.   Conceptually it can be argued that multiple-value identity

   is a natural extension of 1-1 identity, but having 1-1 identity is sometimes useful for a simple-minded optimization.

   I don't strongly suggests identity should be 1-1, but since we already have values, I don't feel the need to use another name, neither.

I would say that restricting a procedure named "identity" to just one value is not the right thing. (As you said, a single-valued version can be helpful for some optimizations, but I wouldn't call it identity.)

One reason why I added the name "identity" was to document that a portable procedure named "identity" should accept an arbitrary number of arguments.

I have no strong opinion about it, though.

 

compose - At least Chicken, SISC and Gauche has "compose", but application order is reversed; that is, (compose f g) is 

   (lambda args (call-with-values (lambda () (apply g args)) f)).  That order also corresponds to the mathematical notation

   of \( f \circ g \).    Srfi-210 uses reverse order for bind etc., so it's not desirable to change only for "compose", but I'd like

   to see it has a different name to avoid confusion.

   Srfi-210 compose is the same order as srfi-189's maybe-compose/either-compose.  In srfi-189 discussion I saw it

   as monadic function composition and didn't think of the conflict of existing "compose".  But srfi-210 is a head-on collision.

   Maybe we should give left-to-right composition a different name.

That's a very unfortunate name-clash. SRFI 210's compose is, of course, a monadic composition much like SRFI 189's maybe-compose (we are talking about the identity monad in the context of SRFI 210). So we should simultaneously change both SRFI 210's and SRFI 189's names for the from-left-to-right composition procedures.

(Added John and Wolfgang as addressees because they created SRFI 189.)

Do you have a good alternative name?

Marc