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Arshia001's solution

to Hangman in the F# Track

Published at Apr 13 2019 · 0 comments
Instructions
Test suite
Solution

Implement the logic of the hangman game using functional reactive programming.

Hangman is a simple word guessing game.

Functional Reactive Programming is a way to write interactive programs. It differs from the usual perspective in that instead of saying "when the button is pressed increment the counter", you write "the value of the counter is the sum of the number of times the button is pressed."

Implement the basic logic behind hangman using functional reactive programming. You'll need to install an FRP library for this, this will be described in the language/track specific files of the exercise.

Running the tests

To run the tests, run the command dotnet test from within the exercise directory.

Further information

For more detailed information about the F# track, including how to get help if you're having trouble, please visit the exercism.io F# language page.

HangmanTest.fs

// This file was created manually and its version is 1.0.0.

module HangmanTest

open Xunit
open FsUnit.Xunit

open Hangman

[<Fact>]
let ``Initially 9 failures are allowed`` () =
    let game = createGame "foo"
    let states = statesObservable game

    let mutable lastProgress = Busy 9
    states.Add(fun state -> lastProgress <- state.progress) |> ignore

    startGame game |> ignore

    lastProgress |> should equal <| Busy 9

[<Fact(Skip = "Remove to run test")>]
let ``Initially no letters are guessed`` () =
    let game = createGame "foo"
    let states = statesObservable game

    let mutable lastMaskedWord = ""
    states.Add(fun state -> lastMaskedWord <- state.maskedWord) |> ignore

    startGame game |> ignore

    lastMaskedWord |> should equal "___"

[<Fact(Skip = "Remove to run test")>]
let ``After 10 failures the game is over`` () =
    let game = createGame "foo"
    let states = statesObservable game

    let mutable lastProgress = Busy 9
    states.Add(fun state -> lastProgress <- state.progress) |> ignore

    startGame game |> ignore

    [for x in 1..10 do makeGuess 'x' game] |> ignore

    lastProgress |> should equal Lose
    
[<Fact(Skip = "Remove to run test")>]
let ``Feeding a correct letter removes underscores`` () =
    let game = createGame "foobar"
    let states = statesObservable game

    let mutable lastState = None
    states.Add(fun state -> lastState <- Some state) |> ignore

    startGame game |> ignore

    makeGuess 'b' game |> ignore

    lastState.Value.progress |> should equal <| Busy 9
    lastState.Value.maskedWord |> should equal "___b__"

    makeGuess 'o' game |> ignore

    lastState.Value.progress |> should equal <| Busy 9
    lastState.Value.maskedWord |> should equal "_oob__"
    
[<Fact(Skip = "Remove to run test")>]
let ``Feeding a correct letter twice counts as a failure`` () =
    let game = createGame "foobar"
    let states = statesObservable game

    let mutable lastState = None
    states.Add(fun state -> lastState <- Some state) |> ignore

    startGame game |> ignore

    makeGuess 'b' game |> ignore

    lastState.Value.progress |> should equal <| Busy 9
    lastState.Value.maskedWord |> should equal "___b__"

    makeGuess 'b' game |> ignore

    lastState.Value.progress |> should equal <| Busy 8
    lastState.Value.maskedWord |> should equal "___b__"
     
[<Fact(Skip = "Remove to run test")>]
let ``Getting all the letters right makes for a win`` () =
    let game = createGame "hello"
    let states = statesObservable game

    let mutable lastState = None
    states.Add(fun state -> lastState <- Some state) |> ignore

    startGame game |> ignore

    makeGuess 'b' game |> ignore

    lastState.Value.progress |> should equal <| Busy 8
    lastState.Value.maskedWord |> should equal "_____"

    makeGuess 'e' game |> ignore

    lastState.Value.progress |> should equal <| Busy 8
    lastState.Value.maskedWord |> should equal "_e___"

    makeGuess 'l' game |> ignore

    lastState.Value.progress |> should equal <| Busy 8
    lastState.Value.maskedWord |> should equal "_ell_"

    makeGuess 'o' game |> ignore

    lastState.Value.progress |> should equal <| Busy 8
    lastState.Value.maskedWord |> should equal "_ello"

    makeGuess 'h' game |> ignore

    lastState.Value.progress |> should equal Win
    lastState.Value.maskedWord |> should equal "hello"
module Hangman

open System

type GameProgress = Waiting | Busy of int | Win | Lose

type Game = {
    mutable progress: GameProgress;
    mutable maskedWord: string;
    word: string;
    stateChanged: Event<Game>
    }

let createGame word = {
    word = word;
    progress = Waiting;
    maskedWord = String.replicate word.Length "_";
    stateChanged = Event<Game>()
    }

let statesObservable game = game.stateChanged.Publish

let updateState game fUpdate =
    fUpdate game
    game.stateChanged.Trigger(game)

let startGame game =
    match game.progress with
    | Waiting -> updateState game (fun g -> g.progress <- Busy 9)
    | _ -> failwith "game already in progress"

let replaceChar str char index = String.mapi (fun i ch -> if i = index then char else ch) str

let playChar (word: string) (maskedWord: string) (char: Char) =
    let rec helper (word: string) (maskedWord: string) (char: Char) (minIndex: int) =
        let index = word.IndexOf(char, minIndex)
        if index < 0 || maskedWord.[index] <> '_' then
            (false, maskedWord)
        else
            let maskedWord = replaceChar maskedWord char index
            let (_, maskedWord) = helper word maskedWord char (index + 1)
            (true, maskedWord)

    helper word maskedWord char 0

let makeGuess char game =
    match game.progress with
    | Busy i ->
        let (anyMatched, newMasked) = playChar game.word game.maskedWord char
        if anyMatched then
            updateState game (fun g -> 
                g.maskedWord <- newMasked
                if g.maskedWord.IndexOf('_') < 0 then g.progress <- Win
                )
        else
            updateState game (fun g ->
                match g.progress with
                | Busy 0 -> g.progress <- Lose
                | Busy n -> g.progress <- Busy (n - 1)
                | _ -> failwith "impossible"
                )
    | _ -> failwith "game not in progress"

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