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Futhark by example (2020)
113 points by tosh 18 hours ago | 31 comments
  • lucb1e
    I was so confused by the word factorial in the first example for a language, but decided to click it and just see what it means

    Turns out, Futhark != https://en.wikipedia.org/wiki/Futhark (runes, old germanic alphabet)

    That's like calling your programming language Latin?! The title could use some disambiguation...

    • hnarn
      > That's like calling your programming language Latin?!

      More accurately it would be like calling it Alphabet, since that takes its name from Alpha Beta (AB) just like the Futhark takes its name from the first letters in it.

    • WJW
      Eh. Words get overloaded all the time and this is a website focusing on programming after all. Would you consider "Python by example" or "C by example" to need disambiguation because they're not about snakes or about the third letter of the alphabet?

      Also the very first line on that page is "The Futhark Programming Language" so if you were still confused after that I think it's on you.

    • pseudohadamard
      It is a pretty confusing name. Personally I'm waiting for someone to name a programming language Womble. Underground, overground, you're free to use it as long as you work as a team and are tidy and clean.
  • ethanlipson
    Futhark is really such a great idea. I'm not convinced that dependent types are worth the cognitive overhead in general, but it's definitely worth it to include the length as part of the type information for dynamic arrays, e.g.:

      concat(Vec<T, n>, Vec<T, m>) -> Vec<T, n+m>
  matmul(Mat<T, n, m>, Mat<T, m, l>) -> Mat<T, n, l>
  head(Vec<T, n+1>) -> (T, Vec<T, n>)
    This would have saved me so much headache debugging CUDA kernels and numpy!! I wish it were a first-class feature in those frameworks, and even general-purpose languages, but alas.
    • itishappy
      Here they are in Futhark:

          val concat [n] [m] 't : (xs: [n]t) -> (ys: [m]t) -> *[n + m]t
    val matmul [n] [m] [l] 't : (xs: [n][m]t) -> (ys: [m][l]t) -> *[n][l]t
    val head [n] 't : (x: [n]t) -> t
      And here's the pathological case (length cannot be determined at compile time):

          val filter [n] 'a : (p: a -> bool) -> (as: [n]a) -> *[]a
      Other pathological cases include conditionals and loops.
    • ainch
      The Pyrefly type checker is starting to work on this kind of shape hinting - so far it only works on Torch but I believe the plan is for it to work with other array packages (eg. JAX, NumPy)

      https://pyrefly.org/en/docs/tensor-shapes/#how-it-works

      • nestorD
        See also jaxtyping which, contrary to what its name might imply, covers JAX/PyTorch/NumPy/MLX/TensorFlow arrays and tensors.

        https://docs.kidger.site/jaxtyping/

      • mathisfun123
        Shape functions and shape analysis are basically mundane infra in almost every ML compiler/language/DSL.

        https://mlir.llvm.org/docs/Dialects/ShapeDialect/

        • ainch
          I didn't know that, thanks for sharing. It makes sense, but then it also makes me wonder why none of the deep learning libraries (Torch, Jax/NNX, Eigen etc...) make this information available. Instead, ML people all have their own schemes for tracking shape information, like commenting '# (b, n, t)' on every line, or suffixing shapes to variable names - and in my experience it's a common source of bugs.
          • mathisfun123
            > Torch, Jax

            Both of these "make it available". Just because people don't know how to use/find them doesn't mean they're not "available".

            > Eigen

            This is not an ML anything, it's a linear algebra library.

            > like commenting '# (b, n, t)' on every line, or suffixing shapes to variable names

            There's a difference between tracking shapes in the compiler and specifying shapes in the model.

    • VorpalWay
      You can do this with templates in C++ and generics in Rust I'm pretty sure. I think the Eigen C++ library supports this. (I have yet to do a linear algebra heavy Rust project, so I can't speak to the options that exist there.)
      • ethanlipson
        I'm talking about cases where the array size is not known at compile time. For example, say the user passes in a list of numbers as command line arguments. Then we have

          argv: Vec<String, argc>
        If I want to map these to ints, then I'd like a compile-time guarantee that the resulting array

          nums: Vec<Int, argc>
        is the same length as argv. Lean and Idris can do this, but AFAIK no commonly used languages can. But unlike general dependent types, these are not hard to wrap one's head around and would save a lot of frustration, in my experience.
      • otabdeveloper4
        Yeah, C++ arrays are literally that.
        • alpinisme
          Arrays are not dynamically sized though (handling runtime sizes) and don’t have efficient append/concat. The point of the dependent types is that you can have the type system track that concat creates an M+N length vector, sort preserves length (and adds a sorted guarantee that slice preserves), etc. Sure you can do a lot with templates, but that’s advanced templates not just “C++ arrays” in a throwaway “literally that” way.
  • Ferret7446
    It would be nice to not name your language after another language. (Yes I know it's a script, that doesn't change my point). I came here expecting something else.
  • fulafel
    Futhark is a glimmer of light in the wasteland of C/C++ styled low level GPU languages.
    • pjmlp
      We also need to have StarLisp back, it would be quite fitting.
  • rowanG077
    Futhark is pretty great! And I have to say that the maintainer is insanely quick. It has happened on more than one occasion that I reported a bug and it's solved within the day. I have been using Futhark in prod for two years now and never had serious problems.
    • keyle
      Interesting, what do use it for if you can share?
      • rowanG077
        Optimization algorithms. The build in automatic differentiation is great!.
    • Reefersleep
      What is your use case?
  • antran22
    Was expecting to see some examples of how to read runes, but I am nonetheless equally satisfied.

    https://en.wikipedia.org/wiki/Elder_Futhark

  • guessmyname
    Couldn’t have chosen a more difficult (and ambiguous) name to pronounce, could you? It almost sounds like a curse that I often hear people say out in the bad streets of New York City.