The Hyperpessimist

The grandest failure.

Reinventing the Semicolon Operator

Lately I was writing some semi-imperative code in OCaml and thinking to myself “man, these ; everywhere sure look ugly”. As I am quite a fan of the |> operator, which threads the execution of multiple functions into a chain: every function gets the result of the application of the previous function, so a |> b |> c corresponds to c (b a).

What I wanted was an operator like |> which throws away the result of the previous function and calls the next function in a normal way. So I named it |-, which coult be used like fun1 |- fun2, which would evaluate to the value of fun2. We could even enforce that the value that fun1 is evaluated to is to be () (unit), so we don’t throw away any important data.

So, let’s implement it:

let (|-) a b =
  a; b

Then it dawned on me: The operator I was looking for existed all along, it is just ;, I can replace all occurences of |- by ;!

This might look like a trivial epiphany, but it has indeed deepened my understanding of the semicolon operator in the language. What I have previously thought of as an purely syntactic element of the language turned out to be an operator in disguise1 and rather unlike how for example Python uses ; (to concatenate multiple expressions into one expression).

  1. Actually, this is not quite true, since ; is indeed syntax, but can be thought as just syntactic sugar for an operator that drops the result of the evaluation of its first argument.