refactored instruction creation

src/parser/instructionFactory.ts

@@ -0,0 +1,19 @@
+/// <reference path="instruction.ts" />
+
+abstract class InstructionFactory
+{
+    private static symbolDict: { [name: string] : Function } = {
+        "point":    (): PointInstruction    => { return new PointInstruction(); },
+        "line":     (): LineInstruction     => { return new LineInstruction(); },
+        "circle":   (): CircleInstruction   => { return new CircleInstruction(); },
+        "len":      (): LengthInstruction   => { return new LengthInstruction(); }
+    }
+
+    public static createInstruction(name: string): Instruction
+    {
+        if(!(name in InstructionFactory.symbolDict))
+            return null;
+
+        return InstructionFactory.symbolDict[name]();
+    }
+}

src/parser/parser.ts

@@ -1,5 +1,5 @@
 /// <reference path="parameter.ts" />
-/// <reference path="instruction.ts" />
+/// <reference path="instructionFactory.ts" />
 
 class Parser
 {
@@ -66,38 +66,11 @@ class Parser
         }
         params.push(paramlist);
 
-        let newInstruction;
+        let newInstruction = InstructionFactory.createInstruction(symbol);
-        switch(symbol)
+        if(newInstruction === null)
         {
-            case "point":
+            console.error("Unknown instruction: \"" + symbol + "\"");
-            {
+            return null;
-                newInstruction = new PointInstruction();
-                break;
-            }
-
-            case "line":
-            {
-                newInstruction = new LineInstruction();
-                break;
-            }
-
-            case "circle":
-            {
-                newInstruction = new CircleInstruction();
-                break;
-            }
-
-            case "len":
-            {
-                newInstruction = new LengthInstruction();
-                break;
-            }
-
-            default:
-            {
-                console.error("Unknown instruction \"" + symbol + "\"");
-                return null;
-            }
         }
 
         let expectedArgs = newInstruction.getParameterCount();