Snake
The classic snake game in the terminal 🐍
Demonstrates:
- game loops
- keyboard controls
- terminal apps
- terminal raw mode
Code
app [main!] { cli: platform "https://github.com/roc-lang/basic-cli/releases/download/0.20.0/X73hGh05nNTkDHU06FHC0YfFaQB1pimX7gncRcao5mU.tar.br" } import cli.Stdin import cli.Stdout import cli.Tty import cli.Arg exposing [Arg] # If you want to make a full screen terminal app, you probably want to switch the terminal to [raw mode](https://en.wikipedia.org/wiki/Terminal_mode). # Here we demonstrate `Tty.enable_raw_mode!` and `Tty.disable_raw_mode!` with a simple snake game. Position : { x : I64, y : I64 } GameState : { snake_lst : NonEmptyList, food_pos : Position, direction : [Up, Down, Left, Right], game_over : Bool, } # The snake list should never be empty, so we use a non-empty list. # Typically we'd use head and tail, but this would be confusing with the snake's head and tail later on :) NonEmptyList : { first : Position, rest : List Position } initial_state = { snake_lst: { first: { x: 10, y: 10 }, rest: [{ x: 9, y: 10 }, { x: 8, y: 10 }] }, food_pos: { x: 15, y: 15 }, direction: Right, game_over: Bool.false, } # Keep this above 15 for the initial food_pos grid_size = 20 init_snake_len = len(initial_state.snake_lst) main! : List Arg => Result {} _ main! = |_args| Tty.enable_raw_mode!({}) game_loop!(initial_state)? Tty.disable_raw_mode!({}) Stdout.line!("\n--- Game Over ---") game_loop! : GameState => Result {} _ game_loop! = |state| if state.game_over then Ok({}) else draw_game!(state)? # Check keyboard input input_bytes = Stdin.bytes!({})? partial_new_state = when input_bytes is ['w'] -> { state & direction: Up } ['s'] -> { state & direction: Down } ['a'] -> { state & direction: Left } ['d'] -> { state & direction: Right } ['q'] -> { state & game_over: Bool.true } _ -> state new_state = update_game(partial_new_state) game_loop!(new_state) update_game : GameState -> GameState update_game = |state| if state.game_over then state else snake_head_pos = state.snake_lst.first new_head_pos = move_head(snake_head_pos, state.direction) new_state = # Check wall collision if new_head_pos.x < 0 or new_head_pos.x >= grid_size or new_head_pos.y < 0 or new_head_pos.y >= grid_size then { state & game_over: Bool.true } # Check self collision else if contains(state.snake_lst, new_head_pos) then { state & game_over: Bool.true } # Check food collision else if new_head_pos == state.food_pos then new_snake_lst = prepend(state.snake_lst, new_head_pos) new_food_pos = { x: (new_head_pos.x + 3) % grid_size, y: (new_head_pos.y + 3) % grid_size } { state & snake_lst: new_snake_lst, food_pos: new_food_pos } # No collision; move the snake else new_snake_lst = prepend(state.snake_lst, new_head_pos) |> |snake_lst| { first: snake_lst.first, rest: List.drop_last(snake_lst.rest, 1) } { state & snake_lst: new_snake_lst } new_state move_head : Position, [Down, Left, Right, Up] -> Position move_head = |head, direction| when direction is Up -> { head & y: head.y - 1 } Down -> { head & y: head.y + 1 } Left -> { head & x: head.x - 1 } Right -> { head & x: head.x + 1 } draw_game! : GameState => Result {} _ draw_game! = |state| clear_screen!({})? Stdout.line!("\nControls: W A S D to move, Q to quit\n\r")? # \r to fix indentation because we're in raw mode Stdout.line!("Score: ${Num.to_str(len(state.snake_lst) - init_snake_len)}\r")? rendered_game_str = draw_game_pure(state) Stdout.line!("${rendered_game_str}\r") draw_game_pure : GameState -> Str draw_game_pure = |state| List.range({ start: At 0, end: Before grid_size }) |> List.map( |yy| line = List.range({ start: At 0, end: Before grid_size }) |> List.map( |xx| pos = { x: xx, y: yy } if contains(state.snake_lst, pos) then if pos == state.snake_lst.first then "O" # Snake head else "o" # Snake body else if pos == state.food_pos then "*" # food_pos else ".", # Empty space ) |> Str.join_with("") line, ) |> Str.join_with("\r\n") clear_screen! = |{}| Stdout.write!("\u(001b)[2J\u(001b)[H") # ANSI escape codes to clear screen # NonEmptyList helpers contains : NonEmptyList, Position -> Bool contains = |list, pos| list.first == pos or List.contains(list.rest, pos) prepend : NonEmptyList, Position -> NonEmptyList prepend = |list, pos| { first: pos, rest: List.prepend(list.rest, list.first) } len : NonEmptyList -> U64 len = |list| 1 + List.len(list.rest) # Tests expect grid_size == 20 # The tests below assume a grid size of 20 expect initial_grid = draw_game_pure(initial_state) expected_grid = """ ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ........ooO.........\r ....................\r ....................\r ....................\r ....................\r ...............*....\r ....................\r ....................\r ....................\r .................... """ initial_grid == expected_grid # Test moving down expect new_state = update_game({ initial_state & direction: Down }) new_grid = draw_game_pure(new_state) expected_grid = """ ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r ....................\r .........oo.........\r ..........O.........\r ....................\r ....................\r ....................\r ...............*....\r ....................\r ....................\r ....................\r .................... """ new_grid == expected_grid
Output
Run this from the directory that has main.roc in it:
$ roc main.roc Controls: W A S D to move, Q to quit Score: 0 .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... ........ooO......... .................... .................... .................... .................... ...............*.... .................... .................... .................... ....................
Run unit tests with roc test main.roc