arity

The arity of a field (value, array [and its arity], list) is not part of the hash of a message definition.

Semicolons separate partial definitions for a single function of a single arity, and periods end those definitions.

First, recur is annoying because functions can have multiple arities, but you can only recur to the same arity.

For better or for worse, muti-arity overloading that doesn't just do partial application is a big part of modern Clojure.

Functions of different arities aren't even type-differentiable (although arity is available as a reflectable value).

So things like calling a function with the wrong arity, and calling a variable/function that doesn't exist are caught at compile time.

List processing via variadic arity functions is an explicit feature of Perl.

But if the choice is between multiple returns (which I guess is just two values?) and tuples, then I don't see why the common case (2-arity) can't be easily supported.

Unless your operators don't have a fixed arity, anyhow (Lisp's don't).

Sadly somebody forgot to keep the arity (variable/tuple/list) in there.

What I was having trouble understanding was why it was being used; specifically, why 'but' would have a strict arity of one in the first place, and why a second function (specifying arity) would be necessary.

I think in Erlang the function identification is the name and the arity and this is as close I know of what you would like to have.

Yet it seems that somehow if I have a bone to pick with Go not being able to dispatch functions by argument or arity, or with how its simplicity ends up with codebases a lot of people would consider much more verbose than necessary, it's just that I don't "get it".

This actually isn't an issue most of the time; since functions' APIs vary so much already (arity, return values, types, etc.) (defmacro unless (condition branch) `(if,condition nil,branch));; Works (unless keep (delete-file "foo.txt")) - Do everything with syntax rewriting!