Why is "reduce" an infix operator in Chapel?

According to this manual page, we can use reduce to perform reduction like summation (+):

var a = (+ reduce A) / num;
var b = + reduce abs(A);
var c = sqrt(+ reduce A**2);

and maximum value/location:

var (maxVal, maxLoc) = maxloc reduce zip(A, A.domain);

Here, Chapel defines reduce to be an infix operator rather than a function (e.g., reduce( A, + )). IMHO, the latter form seems to be a bit more readable because the arguments are always separated by parentheses. So I am wondering if there is some reason for this choice (e.g., to simplify some parallel syntax) or just a matter of history (convention)?

Solution

I'd say the answer is a matter of history / convention. A lot of Chapel's array and domain features were heavily inspired by the ZPL language from the University of Washington, and I believe this syntax was taken reasonably directly from ZPL.

At the time, we didn't have a notion of passing things like functions and operators around in Chapel, which is probably one of the reasons that we didn't consider more of a function-based approach. (Even now, first-class function support in Chapel is still somewhat in its infancy, and I don't believe we have a way to pass operators around).

I'd also say that Chapel is a language that generally favors syntax for key patterns rather than taking more of a "make everything look like a function / method call" approach (e.g., ranges are supported via a literal syntax and several key operators rather than using an object type with methods).

None of this is to say that the choice was obviously right or couldn't be reconsidered.