4 ms·

> knocking together a small lambda calculus + dependently typed interpreter in C. Not ML, Not Ocaml, not, Haskell, not any language that is _already_ got lambda

• Silhouette 11y ago
  The flip side of this is that if you're writing something in C, you actually do have to understand how details like closures are implemented on real hardware. These are not trivial problems, yet many programming language design papers and articles effectively brush the whole issue of actually implementing these things under the carpet. Go ahead and search for that particular example. There is almost nothing on the Web about practical, real world techniques for implementing that sort of programming language feature, despite its ubiquity in functional languages and the increasing presence of -- or emphasis on -- higher order functions and related tools in mainstream imperative languages. The same could be said of many other non-trivial language features, say laziness, or various concurrency models. I think this is regrettable, because it creates a real barrier for anyone who's interested in learning about these features and maybe writing their own languages one day, but who doesn't come from an academic background where this kind of material was taught. It also makes it unnecessarily difficult for someone from an imperative programming background -- which is probably still the overwhelming majority of programmers -- to understand the real costs and performance implications of using these kinds of features.
  • exDM69 11y ago
    > The flip side of this is that if you're writing something in C, you actually do have to understand how details like closures are implemented on real hardware. If you're writing a compiler targeting real hardware and not a high level virtual machine, you'll need to learn how to implement closures regardless of the "host" language you write your compiler in. But you're correct, when implementing an interpreter, it's so much easier if you have a garbage collector and an object system of some kind at hand. You'll have to implement this yourself if you're working with C.
    • Silhouette 11y ago
      If you're writing a compiler targeting real hardware and not a high level virtual machine, you'll need to learn how to implement closures regardless of the "host" language you write your compiler in. Right, but a lot of the tutorial material in this area doesn't really consider that issue, even though it's rather fundamental to practical applications. Instead the explanation often settles for some sort of indirect dependency on the implementation language's existing version of a similar feature. I think this is unfortunate, not least because it reduces us to a model where most people implementing these ideas depend on some sort of magic run-time environment instead of learning how to actually write that run-time.
      • ufo 11y ago
        Thats because tutorial material is going to keep things simple. If you really want to implement a garbage collector on your own then you should go looking for an advanced compiler book instead of a tutorial.
  • jules 11y ago
    You can also implement an interpreter in Haskell/ML without using closures to implement closures. It would still be a lot less painful than C.
    • Silhouette 11y ago