alt Hacker NewsYou get this for free in Haskell, and you also save on not having to remember useless terminology for something that has no application on their own outside Foldables anyways.
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It goes beyond a foldable, can be applied to streams. Clojure had foldables, called reducers, this was generalized further when core.async came along - transducers can be attached to core async channels and also used in places where reducers were used. The terminology is used to document the thing that various contexts accept (chan, into, sequence, eduction etc). They exist to make the language simpler and more general. They could actually allow a bunch of old constructs to be dispensed with but came along too late to build the whole language around.
> You get this for free in Haskell,
Oh, my favorite part of the orange site, that's why we come here, that's the 'meat of HN' - language tribalism with a technical veneer. Congratulations, not only you said something as lame as: "French doesn't need the subjunctive mood because German has word order rules that already express uncertainty", but you're also incorrect factually.
Haskell's laziness gives you fusion-like memory behavior on lists for free. But transducers solve a broader problem - portable, composable, context-independent transformations over arbitrary reducing processes - and that you don't get for free in Haskell either.
Transducers exist because Clojure is strict, has a rich collection library, and needed a composable abstraction over reducing processes that works uniformly across collections, channels, streams, and anything else that can be expressed as a step function. They're a solution to a specific problem in a specific context.
Haskell's laziness exists because the language chose non-strict semantics as a foundational design decision, with entirely different consequences - both positive (fusion, elegant expression of infinite structures) and negative (space leaks, reasoning difficulty about resource usage).
>...you also save on not having to remember useless terminology...
It may be true in this particular case, but in my admittedly brief experience using Haskell you absolutely end up having to remember a hell of a lot of useless terminology for incredibly trivial things.