It occurred to me today that join and List::Util reduce are not only similar functions, but they operate in separate problem spaces. The first argument to join is a string; the first argument to reduce is a coderef. So I thought that it would be a useful improvement to Perl to make join behave like reduce if you pass it a coderef.

Is there any reason that would be a bad idea? Is it an appealing idea? Worth submitting to P5P?

Update: Having received some input, I can flesh out the proposal a bit. I propose that there be a join BLOCK LIST form that would be easily distinguishable from the join LIST form with no possibility of affecting existing code.

The proposal to add reduce as a built-in has already been rejected by P5P on the grounds that it could break existing code. My proposal would not do so. So while reduce is a better name, going that route is a non-starter. My proposal is a zero-impact alternative.

The argument that it's a completely unrelated (or too dissimilar) to the old join has some merit, but it's a matter of perspective. There's a string-join and a functional-join. Both put the separator between all the elements of the list. String-join concatenates the whole mess; functional-join effectively evaluates it as a big expression (where the BLOCK acts essentially like an infix operator). Considering that string-join is a special case of reduce, it is not too much of a stretch (IMO) to have a specific and a general form with the same name.

Caution: Contents may have been coded under pressure.

In reply to RFC: Should join subsume reduce? by Roy Johnson

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