tugofwar

Tug of war

From the basic directory of your fork, create a new project with the following command:

dune init project tugofwar

The main routine in bin/main.ml reads a line from the stdin. The expected format is a sequence of symbols A, B, and =, like e.g.:

AAAAA===BB

This string represents a tug of war game. The leftmost part represents the players of the team A, the symbols = represent the rope, and the rightmost part represents the players of the team B. The winner of a game is the team with the most players.

As you see from the main routine:

let () = match read_line () with
    Some s -> let l = toklist_of_string s in
    if valid l then print_endline (string_of_winner (win l))
    else print_endline "bad input"
  | None -> print_endline "no winner"

you must implement the four missing functions:

• toklist_of_string transforms the input string into a list of tokens A, B, X
• valid determines if a list of tokens is valid, i.e. it belongs to the language A*=*B*
• win determines the winner of a game (token A if the winner is team A, token B if the winner is team B, and X for a tie)
• string_of_winner transforms a token into a string.

Hint: you can use the following function to convert a string into a list of char:

let explode s =
  let rec exp i l =
    if i < 0 then l else exp (i - 1) (s.[i] :: l) in
  exp (String.length s - 1) []

Check the file lib/tugofwar.ml for the signature of these functions,
complete their implementation, and then test the project using dune exec tugofwar.

Recall that you can use the command:

dune utop lib

from the tugofwar directory to test the functions. To use it, first open the Tugofwar library with:

open Tugofwar;;

or write the line in the file tugofwar/.ocamlinit.