Transducers

[lilactown]

Background

Moving this from slack to an issue.

In Clojure, transducers are created by calling core seq functions without the collection, e.g. (map inc), (filter even?). While convenient (no new names needed, no new requires needed), it also adds a couple of challenges:

1. Programming errors emerge that aren't caught by simple arity checking, e.g. (first (map inc))
2. Transducer code can't be tree shaken if one uses (map inc coll)

The first can be caught by better static analysis (clj-kondo) but the second is hard for existing tooling to do.

I proposed two different provocative solutions in slack:

• what if we only had transducers, and eschewed map filter with the collection passed in?
• what if we moved transducers to its own namespace?

Initial response to the first was that it would be too unfamiliar to people coming from Clojure(Script), but that the second would be a good one to try.

Proposal

We add a new namespace, clava.transducers which would hold the transducer protocol and transducing functions.

Transducers would be objects that satisfy the transformer protocol, allowing them to interop with other libraries like Ramda.

We could build it in JS, however I'm interested in trying to build it in Clava source. This would necessarily force us to build and exercise #21.

Feedback welcome!