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by bjz_ 4260 days ago
Rust was first conceived by an avid Ocamler, and it was originally implemented in Ocaml too. Although the pot has been stirred quite a bit since those early days, the influence still remains, including the expression heavy programming style, pattern matching, 'let's, HM inference, and `var: T` declaration syntax. Whilst Rust is quite procedural and (you rarely use recursion), it often feels quite functional due to those things.
1 comments
steveklabnik 4260 days ago
Small note, technically Rust never did HM, and now we _certainly_ don't. It's still inference, just not that algorithm.
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bjz_ 4260 days ago
Oh - I thought it was a variant on HM, extended for region inference?
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steveklabnik 4260 days ago
I'm not _totally_ sure, but I do know when I tried to reference HM in the docs I got yelled at... and now I'm pretty sure we do http://smallcultfollowing.com/babysteps/blog/2014/07/09/an-e...
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kibwen 4260 days ago
It wasn't strictly HM, as it had extensions for the subtyping that lifetimes require. It was based on HM, however.

The new bespoke scheme gives approximately the same results as HM but is drastically simpler. For all I know this could inhibit Rust's future ability to do even more powerful things with types, but AIUI this scheme has the advantage of being actually decidable given the extensions to HM that we would require in the current language.

I ain't a type theorist though, so take this as hearsay. :)

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thinkpad20 4260 days ago
Strictly speaking, I think almost no extant languages, and certainly no mainstream ones, use pure HM, but many take it as a starting point. Certainly, HM has no notion of ML modules, or type classes, or record types, or lifetimes. Nevertheless many languages using those things use HM as a starting point.

I'm curious (and a bit skeptical) of your claim that the scheme is "drastically simpler" than HM. HM is a beautifully simple design, which can be expressed (abstractly) in just a couple of lines.

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kibwen 4260 days ago
I'm paraphrasing Niko Matsakis, Rust's type guru.

http://smallcultfollowing.com/babysteps/blog/2014/07/09/an-e...

"This scheme simplifies the code of the type inferencer dramatically and (I think) helps to meet our intutions (as I will explain). It is however somewhat less flexible than the existing inference scheme, though all of rustc and all the libraries compile without any changes."

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