What is "special" is that the system has a peculiar property: f(x) != f(x).

If we claim to be subscribed to denotational (Mathematical) semantics then the above contradicts the identity axiom.

And it's not any deep and world-changing insight either - it's obvious to anybody who sees that the LHS and RHS are only evaluated at runtime - they don't have any inherent (denotational) meaning, which is why I keep harping on: programmers use different semantics to mathematicians. We care about things like interaction and control flow structures as first class citizens - those are precisely the things that have no mathematical equivalents. Timeouts, exceptions, retry loops.

It's not "syntactic sugar" - it's necessity for reifying control flow. In the words of the (late) Ed Nelson: The dwelling place of meaning is syntax; semantics is the home of illusion.

https://web.math.princeton.edu/~nelson/papers/rome.pdf