OCaml Programming: Correct and Efficient and Beautiful

Post by thingification » Fri, Jun 24, 2022, 7:26 PM UTC

imajoredinecon wrote: post #55

tgflynn wrote: post #51

Earlier quoted context omitted.

It doesn't look so bad to me. It's telling you that a list type was expected but you passed it a function that returns a list instead. You're right though that OCaml isn't the kind of language you can pick up in an afternoon.

Tiny quibble that I wouldn’t normally post but I think illustrates the readability issues here: Should that be “Result set type was expected”, not “list”?

Post by tgflynn » Fri, Jun 24, 2022, 7:30 PM UTC

octachron wrote: post #123

tgflynn wrote: post #59

This is a very specific question but I thought I'd ask it here on the chance someone might have a good answer. I've been slowly working my way through this course and I ran into an issue recently when I upgraded my OCaml installation to the latest version (4.13.1). With this version I find that the simple instructions for building an executable with dune (especially one that uses OUnit) given here https://cs3110.gith…

You can add a dune-project file at the root of your project with just `(lang dune 3.2)` (or your dune version rather than 3.2). The file can also be generated by "dune init project project_name" for fresh projects.

Post by frou_dh » Fri, Jun 24, 2022, 7:36 PM UTC

toolslive wrote: post #116

raverbashing wrote: post #84

"beautiful" But then it has quirks like using ;; to end statements (EDIT: only in the REPL). And comments with that weird syntax But worse of all are the optional parenthesis in function calls. Yes, I know Ruby has it. But it feel super weird and a needless flexibility (that causes more confusion than it solves). I can't get over this stuff, sorry.

> worst of all are the optional parenthesis in function calls ?? > let r = some_function x y z in ... There are no parentheses here, and it's not optional. What you probably are missing is that if `some_function` takes 3 arguments, then `some_function x y` is a function value that takes 1 parameter (currying). Btw, iirc, SML doesn't have this: there you only have 1 parameter but it could be a tuple

Post by abathologist » Fri, Jun 24, 2022, 8:12 PM UTC

whimsicalism wrote: post #107

muglug wrote: post #45

Earlier quoted context omitted.

yes, that would be a straightforward error message! But I got the error message Error: This expression has type ((locl_ty * Tast.pos * ('ex, 'fb, 'en) Aast.expr_) list -> Result_set.t) list but an expression was expected of type Result_set.t list Type (locl_ty * Tast.pos * ('ex, 'fb, 'en) Aast.expr_) list -> Result_set.t is not compatible with type Result_set.t Which is not half as readable.

This seems exactly the same to me just with more complicated type names.

    let f : int -> int = fun _ -> 1 ;;
    val f : int -> int = 
    let ex : int list = [f] ;;
    Line 1, characters 21-22:
    Error: This expression has type int -> int but an expression was expected of type
      int

Post by shikoba » Fri, Jun 24, 2022, 8:51 PM UTC

c-cube wrote: post #148

shikoba wrote: post #109

Earlier quoted context omitted.

I see, you made the beginner mistake with OCaml. You should never read the OCaml error message except if all other options failed. Try to not read those messages, but just look at the line where the error occured. You can use -annot or -bin-annot when compiling and the Tuareg function caml-types-show-type in Emacs will be your best friend.

This is old advice :-). Use the LSP server and dune and the error displays instantly, no further setup required.