ocaml

问题 I am learning Jason Hickey's Introduction to Objective Caml. Here is an exercise I don't have any clue First of all, what does it mean to implement a dictionary as a function ? How can I image that? Do we need any array or something like that? Apparently, we can't have array in this exercise, because array hasn't been introduced yet in Chapter 3 . But How do I do it without some storage? So I don't know how to do it, I wish some hints and guides. 回答1: I think the point of this exercise is to

问题 Could someone explain what the |> operator does? This code was taken from the reference here: let m = PairsMap.(empty |> add (0,1) "hello" |> add (1,0) "world") I can see what it does, but I wouldn't know how to apply the |> operator otherwise. For that matter, I have no idea what the Module.() syntax is doing either. An explanation on that would be nice too. 回答1: Module.(e) is equivalent to let open Module in e . It is a shorthand syntax to introduce things in scope. The operator |> is

问题 I'm working on llvm OCaml bindings. I installed llvm package through opam ( opam install llvm ), when I use llvm in utop, I get the following error: #require "llvm";; Error: The external function 'llvm_global_succ' is not available. The opam llvm version is 3.2. I also tried building llvm3.3 from the official site ( ./configure --with-ocaml-libdir='ocamlc -where' ), the build was successful (all the llvm command-line tools are working), but I got the same error in utop. I'm on Mac OS 10.7.5.

问题 In OCaml, I was used to writing code which looked like: let combine o1 o2 = match o1, o2 with | Valid, Invalid | Invalid, Valid -> Invalid | _ -> ... I didn't find a way to write or-patterns in Haskell and I really miss it. Does anyone have a solution? 回答1: I don't think this is possible in haskell. There are however, a few alternatives: Factor out the common code with a where binding This doesn't make much sense in your example, but is useful if you have more code in the body of the case

问题 I've heard that "first class modules" are coming in OCaml 3.12. What advantages will they offer? What kids of things will be easier? What problem are they trying to solve? A simple example would suffice. 回答1: It's only one possible applications, but first class modules make it easy to encode existential types, with basically a module packing an existential type and a value using this type). For example, See Alain Frisch work on Dynamic types (code taken from Alain Frisch work on dyntypes :

问题 I'm hoping to use either Haskell or OCaml on a new project because R is too slow. I need to be able to use support vectory machines, ideally separating out each execution to run in parallel. I want to use a functional language and I have the feeling that these two are the best so far as performance and elegance are concerned (I like Clojure, but it wasn't as fast in a short test). I am leaning towards OCaml because there appears to be more support for integration with other languages so it

问题 I have two files: myUnionFind.ml and myUnionFind_test.ml . Both files are in the same directory . myUnionFind.ml open Batteries module type MyUnionFindSig = sig type union_find val print_array : 'a array -> unit val create_union : int -> union_find val union_weighted : union_find -> int -> int -> unit val is_connected_weighted : union_find -> int -> int -> bool end;; module MyUnionFind : MyUnionFindSig = struct let print_array ary = print_endline (BatPervasives.dump ary);; type union_find =

问题 I want to write a function that takes in a sequence <1,1,2,2,3> and returns the sequence with equal elements grouped like <<1,1>, <2,2>, <3>>. I'm using sequences, not lists, but some of the functions are similar. Some of the functions I am thinking of using are map, reduce, tabulate, filter, append etc.. Reduce takes in an associative function and returns the sequence that is "reduced" by that operator. So, reduce op+ 0 <1,2,3> = 6. My first thought was to use map to raise the sequence by

问题 I am experimenting with Core's List.fold_left . # List.fold_left;; - : 'a Core.Std.List.t -> init:'b -> f:('b -> 'a -> 'b) -> 'b = <fun> It works fine when I specify the labels: # List.fold_left [1;2;3] ~init:0 ~f:(+);; - : int = 6 But I get a different result when I do not specify the labels: # List.fold_left [1;2;3] 0 (+);; - : init:(int -> (int -> int -> int) -> '_a) -> f:((int -> (int -> int -> int) -> '_a) -> int -> int -> (int -> int -> int) -> '_a) -> '_a = <fun> And other partial

问题 I have a very short test file: let print_backtrace () = try raise Not_found with Not_found -> Printexc.print_backtrace stdout;; let f () = print_backtrace (); Printf.printf "this is to make f non-tail-recursive\n";; f (); I compile and run: % ocamlc -g test.ml % OCAMLRUNPARAM=b ./a.out Raised at file "test.ml", line 1, characters 35-44 this is to make f non-tail-recursive Why isn't f listed in the stack trace? How can I write a function that will print a stack trace of the location it's