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projects/12/Keyboard.jack

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+// This file is part of www.nand2tetris.org
+// and the book "The Elements of Computing Systems"
+// by Nisan and Schocken, MIT Press.
+// File name: projects/12/Keyboard.jack
+
+/**
+ * A library for handling user input from the keyboard.
+ */
+
+class Keyboard {
+    static Array mem;
+    /** Initializes the keyboard. */
+    function void init() {
+        let mem = 0;
+        return;
+    } 
+
+    /**
+     * Returns the character of the currently pressed key on the keyboard;
+     * if no key is currently pressed, returns 0.
+     *
+     * Recognizes all ASCII characters, as well as the following keys:
+     * new line = 128 = String.newline()
+     * backspace = 129 = String.backspace()
+     * left arrow = 130
+     * up arrow = 131
+     * right arrow = 132
+     * down arrow = 133
+     * home = 134
+     * End = 135
+     * page up = 136
+     * page down = 137
+     * insert = 138
+     * delete = 139
+     * ESC = 140
+     * F1 - F12 = 141 - 152
+     */
+    function char keyPressed() {
+        return mem[24576];
+    }
+
+    /**								
+     * Waits until a key is pressed on the keyboard and released,
+     * then echoes the key to the screen, and returns the character 
+     * of the pressed key.
+     */
+    function char readChar() {
+        var char a, b;
+        do Output.printChar(0);
+        while ((b = 0) | (a > 0)){
+            let a = Keyboard.keyPressed();
+            if (a > 0){
+                let b = a;
+            }
+        }
+        do Output.printChar(String.backSpace());
+        do Output.printChar(b);
+        return b;
+    }
+
+    /**								
+     * Displays the message on the screen, reads from the keyboard the entered
+     * text until a newline character is detected, echoes the text to the screen,
+     * and returns its value. Also handles user backspaces.
+     */
+    function String readLine(String message) {
+        var String s, b;
+        var char c;
+        let s = String.new(100);
+        do Output.printString(message);
+        while (true){
+            let c = Keyboard.readChar();
+            if (c = 128){
+                return s;
+            }
+            else{
+                if (c = 129){
+                    do s.eraseLastChar();
+                }
+                else{
+                    do s.appendChar(c);
+                }
+            }
+        }
+        return;
+    }   
+
+    /**								
+     * Displays the message on the screen, reads from the keyboard the entered
+     * text until a newline character is detected, echoes the text to the screen,
+     * and returns its integer value (until the first non-digit character in the
+     * entered text is detected). Also handles user backspaces. 
+     */
+    function int readInt(String message) {
+        var starting a;
+        var int b;
+        let a = Main.readLine_stolen(message);
+        let b = String.intValue(a);
+        do String.dispose(a);
+        return b;
+    }
+}