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F*: A general-purpose proof-oriented programming language
125 points by ducktective 8 hours ago | 48 comments
  • cyanregiment
    Clicked like 5 pages and never found 1 code example.

    Idk why languages don't have their syntax in a sandbox front-and-center on the home page.

    It's like a video game site with zero screenshots or videos (also rampant).

    New programming languages I want 2 things:

    1. What does the syntax look like

    2. Why would I use this language

    Talk about the proof logic, show the syntax, thank you

    • Verdex
      To borrow your video game analogy. F* is the dwarf fortress of programming languages. Screenshots are only going to confuse anyone who isn't ready to take a significant mental journey.
      • redrobein
        This is needless fearmongering. F* looks a lot like F# code with semantics you should be familiar with if you've worked with other proof oriented languages. The website design is dated is all. The book gives exactly what the OP wants in the introductory chapter.
    • rixed
      I'm the opposite: when landing in a programming language site I want to know the user case the authors had in mind, the memory model, the type system, the compilation targets, the data layout, the control structures, and only at the end just check that the syntax is not indentation based.
      • sroerick
        So I'm very seriously considering making my language indentation based. You're saying you wouldn't like that?
        • Georgelemental
          Indentation based is a pain when copy-pasting between contexts with different indentation levels, as you have to fix it up manually, which is error-prone. In languages without it, you can just auto-format. (And even in an editor that doesn't support that, having a second indicator makes it less error-prone to fix manually)
        • rixed
          No indeed I'm not a fan. I find it brittle and arbitrary for data values especially; that also makes automatic code generation and edition harder, for no good reason. But that's not an important consideration either way.
          • NuclearPM
            What is code edition?
            • aleph_minus_one
              > What is code edition?

              I think rixed means "code editing" (I guess that rixed is simply not a native (L1) or excellent L2 English speaker).

        • mcluck
          For what it's worth, I love the semantics of many indentation based languages (F# for example) but really dislike editing them. Visually scanning is much easier with braces (imo) and it's much easier to navigate braced languages when using a vim-like editor
        • dunham
          I don't mind indentation based languages. I used to hate them, but they've grown on me after using python, Haskell, Idris, Agda, etc. And I ended up making my own language indentation based (it is similar to Idris).

          That said, it is hard-mode:

          - You'll have to figure out how to parse it.

          - If you want editor support, it's a pain to get tree-sitter to handle it.

          - You may not be able to pull off editor operations like "rename" without implementing a pretty printer (a rename might affect indentation).

          I think it is helpful for crude error recovery. On parse error, my language will simply skip to the next column 0 token and parse another declaration.

          I did not do this (hindsight), but I would recommend arranging the grammar so you only get indented blocks in cases where the previous line ends in a keyword that introduces it. I think python has a trailing `:` every time indentation is introduced, and Elm does this too - in statements like `let` you need a newline after the `let` to get the multi-declaration version. (This addresses the rename issue.)

        • zlsa
          I think this falls under "[wanting] to know the user case the authors had in mind"
          • BretonForearm
            There is no "user case", it's called use case.
            • aleph_minus_one
              > There is no "user case", it's called use case.

              Perhaps English is not a native language for zlsa?

        • giancarlostoro
          I love that people hate indentation based so I show them a poorly indented C style languages codebase to see how they feel about indentation.
          • koolala
            Isn't it easy to just auto format it?
      • NuclearPM
        Use case. Not “user case”.
    • kasumispencer2
      > Clicked like 5 pages and never found 1 code example.

      But I clicked one (1) link to the online book and found a thousand?

      • giancarlostoro
        Should be on the home page of any programming language site.
        • kasumispencer2
          Is there actually any difference when it's just one (1) link away? Are most of us seriously this busy that we cannot spend even half a minute on this?
          • broken-kebab
            There's a difference, yes. How big it is isn't really relevant question cause its simply an unnecessary tax on visitors.
    • munchler
      https://fstar-lang.org/tutorial/
      • _flux
        I guess it's a bit popular right now

            * Error 17 at Welcome.fst(24,0-28,30):
      - Could not start SMT solver process.
      - Command: ‘/home/site/wwwroot/fstar/bin/z3’
      - Exception:
          Unix.Unix_error(Unix.ENOENT, "create_process", "/home/site/wwwroot/fstar/bin/z3")
    
    1 error was reported (see above)
      • aleph_minus_one
        > https://fstar-lang.org/tutorial/

        FYI: The link to this tutorial is unluckily a little bit obscured on the F* website: Go to

        > https://fstar-lang.org/index.html#learn (1)

        and click on the image below the text "You probably want to read it while trying out examples and exercises in your browser by clicking the image below.".

        In the section of (1) also the PDF version is linked:

        > https://fstar-lang.org/tutorial/proof-oriented-programming-i...

        • cyanregiment
          I still don't see any code examples!

          But I do see the editor to try it.

          I wonder why more languages don't have a few simple examples of: "HTTP server", "hello world", "todo list app" that you can just click and it shows the code for how you'd make it in that language.

          It matters a lot how the syntax looks IMO and seeing how, say, an API is scaffolded, helps understand a lot about the language in one glance

          Edit: Page 18 of the PDF. That's the first time I found what the code looks like, thanks for sharing!

          • aleph_minus_one
            > I wonder why more languages don't have a few simple examples of: "HTTP server", "hello world", "todo list app" that you can just click and it shows the code for how you'd make it in that language.

            Often the reason is that the value that the programming language brings is thinking very differently about how to write code - the examples how to write something in it are merely the "more boring" consequences of this different way of thinking.

            --

            If you want a programming language that "just" enables you to write something well-understood (in particular in the area of web development) like your suggested

            > "HTTP server", "hello world", "todo list app"

            in a perhaps just a little bit more elegant/concise way, just look at which web development language/framework is currently fashionable on HN.

            • cyanregiment
              > just look at which web framework

              See, by listing those, you can tell what it is.

              I imagine the quick project showcase would be different for Swift or for Rust.

              Would be nice to have something like that for this Fstar or any language I haven’t heard of - or maybe have but never looked into so I see why people are using it.

              Like what kinds of things i can even think of writing with it - an implementation example

              • aleph_minus_one
                > I imagine the quick project showcase would be different for Swift or for Rust.

                > Would be nice to have something like that for this Fstar or any language I haven’t heard of - or maybe have but never looked into so I see why people are using it.

                I suggest simply having a look at the table of contents of

                > https://fstar-lang.org/tutorial/proof-oriented-programming-i...

                This in my opinion gives you a first rough idea for what kind of problems people are using F*.

                Spoiler alert: these are not the kind of problems which are related to ["HTTP server", "hello world", "todo list app", ...].

                This is exactly the reason why I wrote further above:

                > Often the reason [why more languages don't have a few simple examples of: "HTTP server", "hello world", "todo list app"] is that the value that the programming language brings is thinking very differently about how to write code - the examples how to write something in it are merely the "more boring" consequences of this different way of thinking.

                • cyanregiment
                  > these are not the kind of problems which are related to ["HTTP server", "hello world", "todo list app", ...].

                  Ok, what kinds of problems are they?

                  And ideally - what does a simple solution look like in F-star?

                  Set me on the path to installing the thing (ideally above the fold)

    • rainyq
      just click the screenshot
      • cyanregiment
        Takes you to an empty editor with still no code examples
    • remywang
      That’s because syntax is the least interesting part of F*.
      • thomastjeffery
        Then why are we all so interested?

        Examples provide more than syntax. It's the semantics that we care about most.

        • aleph_minus_one
          > Examples provide more than syntax. It's the semantics that we care about most.

          ... and this semantics is explained in a quite encompassing way in the introductory notes "Proof-Oriented Programming in F*":

          > https://fstar-lang.org/tutorial/proof-oriented-programming-i...

          > https://fstar-lang.org/tutorial/

          • derdi
            The OP doesn't want encompassing, they want the following example from the tutorial on the front page:

                type vec (a:Type) : nat -> Type =
      | Nil : vec a 0
      | Cons : #n:nat -> hd:a -> tl:vec a n -> vec a (n + 1)
    
    let rec append #a #n #m (v1:vec a n) (v2:vec a m)
      : vec a (n + m)
      = match v1 with
        | Nil -> v2
        | Cons hd tl -> Cons hd (append tl v2)
            This is a completely reasonable thing to want and expect.
    • qzzi
      I clicked on 2 links on the main page in the Learn F* section...
    • voodooEntity
      Thank you ! I just had the absolute same experience and was about to write a similar comment - take my upvote instead !
    • summarity
      What? There’s literally a completely interactive book linked right from the home page.
  • pvsnp
    I liked being able to express calling external libraries while incrementally migrating existing C codebases to F*. Very solid language.
    • rixed
      What do you mean "express calling"? You mean calling the former C versions of the functions not yet ported, while asserting their behavior?
  • LelouBil
    I like Haskell, and to me this seems really useful as a kind of "noob" to functional languages.

    Is this used in the industry ? And for what kind of software ?

  • boutell
    I guess responsive stylesheets can't be implemented without side effects...
  • 3lambda
    Would this language be useful for implementing compilers and formally proving things about them?
    • physPop
      yes thats the main reason, agda , coq similar ideas
  • IshKebab
    F* seems to be a collection of like five different languages and proof systems. Honestly I never figured it out.

    Does it get basic stuff like subtraction and u8 right, unlike Lean?

  • kirlfiend_grill
    [flagged]