Implemented extension logic

levels.ts

@@ -1,26 +1,38 @@
 //% color=#20bf6b weight=100 icon="\uf0ae"
 namespace levels {
 
+    let currentLevel: number = 1;
+    const levels: Array<() => void> = [];
+
     /**
     Change the current level that is playing
     **/
     //% block
     //% l.defl=1
     export function startLevel(l: number = 1) {
+        currentLevel = l;
+        const handler = levels[l];
+        if (handler) {
+            handler();
+        } else {
+            console.error("ERROR: No 'on start level' block found for level " + l);
+        }
     }
 
     /**
     Restart the current level
     **/
     //% block
     export function restartLevel() {
+        startLevel(currentLevel);
     }
 
     /**
     Start the next level (increment level by one)
     **/
     //% block
     export function startNextLevel() {
+        startLevel(currentLevel + 1);
     }
 
     /**
@@ -30,5 +42,6 @@ namespace levels {
     //% block="on start level $l"
     //% l.defl=1
     export function onStartLevel(l: number = 1, handler: () => void): void {
+        levels[l] = handler;
     }
 }

main.blocks

@@ -1 +1 @@
-<xml xmlns="https://developers.google.com/blockly/xml"><block type="pxt-on-start" id="@!{Ymfd?WLn82.Z50V$L" x="0" y="0"></block></xml>
+<xml xmlns="https://developers.google.com/blockly/xml"><block type="pxt-on-start" id="i64~^za7|!w^;/Hc?nc6" x="0" y="0"></block></xml>