drnewman

Nice explanation

I’ll check it out. Thank you.

I would say more broadly the innovation was two fold: 1) to make these features available in a syntactic form that would seem more familiar to programmers and 2) the powerful insight that when combined with Smalltalk style meta programming you can have a language that on the surface seems very conventional but underneath is just as powerful as Smalltalk or Lisp.

Although I would say he didn’t get 100% there although that this point Ruby isn’t too far from that.

These are ideas that I think are worth trying to take even further. In fact, I’ve been experimenting with that.

I agree blocks are closures. But they’re call stack aware closures. Which gives them _some_ of the power of continuations.

I’m also sure you’re right that they’re not implemented using continuations. However, my understanding is that Ruby was originally conceived as a language with continuations. I’ll see if I can find a reference for that. But from what I recall reading in a blog post from someone who was at a programming language conference in 1997 when Matz introduced the language that’s how he described it.

Yes Smalltalk has continuations. So it can do all of those things as well. But I don't think they're explicitly tied to blocks like they are in Ruby. This really isn't a problem for Smalltalk since it's not as syntax oriented as Ruby.

The invovation is to have those features tied to convenient syntax.

I'd think the preferred way would be to implement them as a separate class. That'd be more in line with the design of other core classes (like TrueClass & FalseClass). It'd also have created the opportunity to create a "Callable" protocol early in the design which would have been great, and would harmonize with the design of Ruby's many other protocols Enumerable, Comparable, Range-compatible values, etc.

Yeah, I think I've heard that too.

That's insightful

Blocks in Smalltalk (to my understanding) are closures. Blocks in Ruby are closures that also bring the call stack they were created in with them.

One way to think of about it is this: anonymous functions as originally implemented in early Lisps are code as an object, closures are code with its lexical environment as an object. You can think of a Ruby block as code with its lexical environment and its call stack as an object.

So they don't just handle return differently than closures, they have access to the call stack of the site where they're created like a continuation. This is why they handle return differently, but this is just one of the things that falls out from that. It also comes with other control flow features like "redo", "retry", "next", "rescue", "finally", and others. These are all call stack control (control flow) conveniences, just like return is. All of them can be thought of as being abstractions built on top of continuations (just ask a Scheme hacker).

Originally Ruby was basically a Lisp without macros, but with continuations, a Smalltalk like object system and a lot of syntactic affordances inspired by Perl, and other languages. Blocks are one of the conveniences built on top of the Lispy semantics.

Note that I'm explaining how blocks work as an abstraction (vidarh below explains how they work as a concretion, as implemented in MRI).

It seems you're pretty upset about your experience with Ruby. I'm sorry that's been the case for you.

However, in Ruby blocks aren't just about flexibility, more importantly they're about generality. They're not there to resolve an edge case at all (Ruby also has keywords for loops). They're a generalization of control flow that is just slightly less general than continuations. In practical use they provide an alterative to Lisp macros for many use cases.

These were some of the problems Matz was trying to sort out with his design of Ruby--creating a language that was fun and easy to use for day-to-day programming, with as much of the meta-programming power of Lisp and Smalltalk as possible. Blocks are one of his true innovatations that came from trying to balance that tension.

Laziness is great for collections, and modeling the infinite but as a general model for programming it's a little loopy for my taste too ;-)