I’m trying to print a specific list, but it doesn’t work let rec listes_paires l = match l with | [] -> [] | x :: r -> if List.length x mod 2 = 0 then (x :: (listes_paires r)) else ((x@x):: (listes_paires r));; List.iter print_int (listes_paires [[]; [1];[1;2];[1;2;3];[];[5;4;3;2;1]]);; Error message says : Line 5,… Read More How to print a list of lists

I run a hello world program below let x=3; print_string "hello world!";; and got this warning: File "hello.ml", line 1, characters 6-7: 1 | let x=3; ^ Warning 10 [non-unit-statement]: this expression should have type unit. How can I fix it? >Solution : Recall from the answers to your previous questions that ; is a… Read More Warning due to semicolon

People say everything in ocaml is an expression and has a type. But how can I understand a statement like let x = 3; and let y = x * x; These do not look like expressions, right? >Solution : OCaml expression are presented here https://v2.ocaml.org/manual/expr.html, and what you have typed is not expressions but… Read More Is "let x = 3;;" an expression?

I am having a problem understanding this particular line let lst = ["a", "b", "c"]; List.filter (fun (a, _b) -> not (List.mem a lst)) assoc >Solution : List.filter takes a function that takes each element in the list in turn and returns a boolean. If the boolean value is true, the element is part of… Read More List.filter and List.mem

I want to convert a matrix(type matrix = float list list) into a list(so basically I’m writing a function to concatenate a list of lists, but I’m not allowed to use List.append, List.flatten, etc.). So for example, into_list [[1.; 2.]; [3.; 4.] = [1.; 2.; 3.; 4.]. I wrote my helper function to append two… Read More Convert a matrix into a list by flattening it ocaml

let rec add_lists (xs : float list) (ys : float list): float list option = match xs ys with | ([],[]) -> Some[] | (x::xs’, []) -> None | ([],y::ys’) -> None | hd::tl -> (match xs ys with |[] -> None |hd2 :: tl2 ->(hd+hd2):: (add_lists tl tl2) ) I wanted to add 2… Read More Adding two list in OCaml

I wrote a simple function to return whether an element is in a list. let rec contains elem l = match l with | a::c -> if (a = elem) then true else (contains elem c) | [] -> false let t = contains "a" ["a"; "b"];; Upon executing this code I get the error:… Read More Type error for a contains element function in OCaml

I have two .ml files, type.ml and main.ml, in the same directory. I am following this official link: https://ocaml.org/docs/modules File main.ml: open Type let () = print_endline "Hello World!" I compile with this line, accordingly to the tutorial: ocamlopt -o main main.ml type.ml However, I have this error: Error: Unbound module Type >Solution : The… Read More Unbound Module (Personal Files)

I’ve been trying to write code to traverse and print any binary tree. However, static typing makes it really difficult. Here is my attempt. However, it tells me Error: This expression has type char but an expression was expected of type printable In the example_tree definition. I totally understand, ‘a’ for example is a char… Read More Any Type ('a) Binary Tree Traversal + Print

Hey I’m new to ocaml and was trying out some of the exercises in a dune build. I think my issue is due to the semicolons but I’m not really sure. When running the following code: let somelist = [1;2;3;4] in (* last element in a list *) match (last somelist) with | Some (v)… Read More Second match block not executing (OCaml)