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POVery simple RogueLike in F#, making it more "functional"
 

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    <p>I have some existing C# code for a very, very simple RogueLike engine. It is deliberately naive in that I was trying to do the minimum amount as simply as possible. All it does is move an @ symbol around a hardcoded map using the arrow keys and System.Console:</p> <pre><code>//define the map var map = new List&lt;string&gt;{ " ", " ", " ", " ", " ############################### ", " # # ", " # ###### # ", " # # # # ", " #### #### # # # ", " # # # # # # ", " # # # # # # ", " #### #### ###### # ", " # = # ", " # = # ", " ############################### ", " ", " ", " ", " ", " " }; //set initial player position on the map var playerX = 8; var playerY = 6; //clear the console Console.Clear(); //send each row of the map to the Console map.ForEach( Console.WriteLine ); //create an empty ConsoleKeyInfo for storing the last key pressed var keyInfo = new ConsoleKeyInfo( ); //keep processing key presses until the player wants to quit while ( keyInfo.Key != ConsoleKey.Q ) { //store the player's current location var oldX = playerX; var oldY = playerY; //change the player's location if they pressed an arrow key switch ( keyInfo.Key ) { case ConsoleKey.UpArrow: playerY--; break; case ConsoleKey.DownArrow: playerY++; break; case ConsoleKey.LeftArrow: playerX--; break; case ConsoleKey.RightArrow: playerX++; break; } //check if the square that the player is trying to move to is empty if( map[ playerY ][ playerX ] == ' ' ) { //ok it was empty, clear the square they were standing on before Console.SetCursorPosition( oldX, oldY ); Console.Write( ' ' ); //now draw them at the new square Console.SetCursorPosition( playerX, playerY ); Console.Write( '@' ); } else { //they can't move there, change their location back to the old location playerX = oldX; playerY = oldY; } //wait for them to press a key and store it in keyInfo keyInfo = Console.ReadKey( true ); } </code></pre> <p>I was playing around with doing it in F#, initially I was trying to write it using functional concepts, but turned out I was a bit over my head, so I did pretty much a straight port - it's not <em>really</em> an F# program (though it compiles and runs) it's a procedural program written in F# syntax:</p> <pre><code>open System //define the map let map = [ " "; " "; " "; " "; " ############################### "; " # # "; " # ###### # "; " # # # # "; " #### #### # # # "; " # # # # # # "; " # # # # # # "; " #### #### ###### # "; " # = # "; " # = # "; " ############################### "; " "; " "; " "; " "; " " ] //set initial player position on the map let mutable playerX = 8 let mutable playerY = 6 //clear the console Console.Clear() //send each row of the map to the Console map |&gt; Seq.iter (printfn "%s") //create an empty ConsoleKeyInfo for storing the last key pressed let mutable keyInfo = ConsoleKeyInfo() //keep processing key presses until the player wants to quit while not ( keyInfo.Key = ConsoleKey.Q ) do //store the player's current location let mutable oldX = playerX let mutable oldY = playerY //change the player's location if they pressed an arrow key if keyInfo.Key = ConsoleKey.UpArrow then playerY &lt;- playerY - 1 else if keyInfo.Key = ConsoleKey.DownArrow then playerY &lt;- playerY + 1 else if keyInfo.Key = ConsoleKey.LeftArrow then playerX &lt;- playerX - 1 else if keyInfo.Key = ConsoleKey.RightArrow then playerX &lt;- playerX + 1 //check if the square that the player is trying to move to is empty if map.Item( playerY ).Chars( playerX ) = ' ' then //ok it was empty, clear the square they were standing on Console.SetCursorPosition( oldX, oldY ) Console.Write( ' ' ) //now draw them at the new square Console.SetCursorPosition( playerX, playerY ) Console.Write( '@' ) else //they can't move there, change their location back to the old location playerX &lt;- oldX playerY &lt;- oldY //wait for them to press a key and store it in keyInfo keyInfo &lt;- Console.ReadKey( true ) </code></pre> <p>So my question is, what do I need to learn in order to rewrite this more functionally, can you give me some hints, a vague overview, that kind of thing. </p> <p>I'd prefer a shove in the right direction rather than just seeing some code, but if that's the easiest way for you to explain it to me then fine, but in that case can you please also explain the "why" rather the "how" of it?</p>
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    1. COthis isn't the easiest task to get started with F#, or functional programming in general. State is pretty inherent to the positioning of the @ sign, and I think doing this in proper functional form would require monads or other arrow constructs.
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    2. CO@jon_darkstar: It's quite possible to implement it without using any constructs like that. In fact, I would recommend implementing the pattern yourself first so that you understand what it's doing before you abstract it away behind a monad.
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    3. COyes, i guess i overthought it a little. now that i read closer it seems OP does know some functional basics, and this exercise would probably serve as a pretty key hurdle to get past. follow this through nrkn, theres some good answers below. this is one of the tougher aspects of FP but youll be better off for it. if you really wanted to implement this in a serious way F# is probably not the best choice, but it looks like you set up a good exercise here.
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