Are "procedure" and "function" synonymous in Racket?

Question

Are "procedure" and "function" synonymous in Racket (a dialect of Scheme)? It seems to be implied by the documentation. For example, the documentation for compose describes it as a procedure that

[r]eturns a procedure that composes the given functions...The compose function allows the given functions to consume and produce any number of values...

(All of the above italicization was added by me.)

I understand that procedure? is a library procedure and function? is not. My question is whether it is correct to use the terms interchangeably when discussing programs (such as when teaching a class or writing documentation).

Answer 1

TL;Dr It's just lingo and means the same. function, procedure, and static method is the same in programming.

Historically a function is in the mathematical sense a mapping between arguments to a result. A procedure is a block of code that does something and its output does not need to be tied to any specific input. Thus you could say a function is a procedure with no side effects.

The Scheme standard uses only the term procedure. You won't find any hints about function at all. Racket is historically a standard Scheme implementation made for education purposes and is pretty much still compatible with Scheme for the most part today, but they have made a split and does not consider themselves to follow a Scheme standard. How to design programs and lots of documentation uses the term function and in this documentation it is meant as a synonym to procedure.

Common Lisp uses the term function consistently and its predecessors too, which predates Scheme.

I think I have even translated a SO answer between languages and changed the code as well as just switched function and procedure for consistency with the languages lingo itself. I would love to see Racket clean up some day and stay with one name to rule them all.

Answer 2

The short version: yes.

The longer version: a number of folks have done good work on aligning vocabulary for use in teaching. This is the first paper that comes to mind, although it does not specifically address the procedure/function choice:

https://cs.brown.edu/~sk/Publications/Papers/Published/mfk-measur-effect-error-msg-novice-sigcse/paper.pdf

From a pedagogic standpoint, of course, it's unhelpful to have two names for the same thing, sigh.

Finally, you'll get a more authoritative answer (and frankly, I'd like to know what the state of things here is) if you ask this question on the Racket Mailing List.

[EDIT] Ooh, further, I would not at all say that the word procedure is more likely to denote something defined in a library.