“Other languages” have this function also seem to be the same languages where every function is arity 1 (what you’d think of as an arity 3 function is just an arity 1 that returns a function that is arity 1 that returns a function that is arity 1 that return the result), and no language on the BEAM can work quite like that without a huge amount of preprocessing to ‘pack’ arity’s together if you want to work with the rest of the beam.

I think this proposal is tricky because, unlike identity/1, there isn’t an obvious arity that your return function should have. Should it be:

fn -> value end
or
fn _ -> value end
or
fn _, _ -> value end
... etc

Each of those has real scenarios where they’d be useful.

The other issue is that these two things do not have the same semantics: Function.constantly(code) and fn -> code end will behave differently depending on what code is. If code is DateTime.utc_now() then Function.constantly will return the same date time over and over, but fn -> DateTime.utc_now() end will return a new datetime each time it is invoked.

Nitpick: Function.constantly(value) is also not a shorter version, since it’s literally nine characters longer.