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Discussion on: Tail Recursion

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gypsydave5 profile image
David Wickes

Ben, you're a nutter (in the nicest way possible). Tail calls in C++ -- I did not see that coming.

I always think of...

from xkcd

But here you've made the point that tail recursion is not its own reward -- it allows an optimization in C++ and other languages. This is so often missed out when people discuss and teach (and perform) functional programming: we're at the mercy of the compiler as to whether what we're writing is at all performant.

Two examples I always think of:

JavaScript

Although the ES2015 spec requires Tail Call Optimization (TCO), it's supported in barely any of the JS run times! Write some recursive JS and your stack will soon blow!

Kotlin

Arrow, a functional library for Kotlin. Because the Kotlin compiler (should that be 'kompiler'?) is built to optimize for imperative code with a souçon of functional sugar, the 'functional' structures that Arrow supplies are woefully less performant than the equivalent imperative code. I have benchmarks... somewhere...


This makes me think that what makes a 'functional language' functional is very little to do with the actual language, but rather what the compiler / interpreter is optimizing for.

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deciduously profile image
Ben Lovy Author

Hah, I've just got C++ on the brain this week! It does optimize for it :) Heaven forbid I stick to a language for two consecutive posts.

I actually didn't know that about JS, way to go Safari. Thanks for pointing that out!

Kotlin has actually been high on my "try-next" list for a while. I had a great time with Clojure, that's one heck of a runtime to be driving, but eventually felt it not practical for what I was working on and Kotlin looks like a great JVM addition a little closer to the mainstream. I'm surprised to hear that there's such a disparity, I thought the langauge was intended to be more functional forward. Do you know if it's a development priority or are most using Kotlin in a more Java-esque style?

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gypsydave5 profile image
David Wickes

Do you know if it's a development priority or are most using Kotlin in a more Java-esque style?

From my experience of it Kotlin is trying to be a less awful Java with excellent interop. Some ideas from Groovy, some from Scala. It's got a good (and necessary) story to tell about nulls.

What it isn't is a language like Haskell or Scala, and I don't think it ever will be (or should be).

But it's definitely better than writing Java.