diff --git a/examples/test.gs b/examples/test.gs
index fa68652..291c48a 100644
--- a/examples/test.gs
+++ b/examples/test.gs
@@ -1,2 +1,9 @@
-[point(3, 4) -> A]
-line(A, point(7, 8))
\ No newline at end of file
+point(0.2378, -34.389) -> A
+point(2.5, 0) -> B
+[point(-1, 3) -> C]
+
+line(A, B) -> AB
+line(B, C)
+line(C, A)
+
+circle(A, len(AB))
\ No newline at end of file
diff --git a/examples/test.gs.disable b/examples/test.gs.disable
new file mode 100644
index 0000000..8b2a065
--- /dev/null
+++ b/examples/test.gs.disable
@@ -0,0 +1,9 @@
+point(-1, 0) -> A
+point(1, 0) -> B
+line(A, B) -> AB
+len(AB) -> length
+circle(A, len(AB)) -> circleA
+circle(B, len(AB)) -> circleB
+intersection(circleA, circleB, 0) -> C
+line(A, C)
+line(B, C)
diff --git a/src/doc/todo.md b/src/doc/todo.md
new file mode 100644
index 0000000..e11c816
--- /dev/null
+++ b/src/doc/todo.md
@@ -0,0 +1,9 @@
+# TODO (Parser)
+* Type checking
+* Ignore case in instruction names
+* Implement remaining functions
+* Abort parsing on error
+
+# TODO (Renderer)
+* Implement shape classes
+* Render shape classes
\ No newline at end of file
diff --git a/src/parser/instruction.ts b/src/parser/instruction.ts
index 67f49c6..d0ee0fd 100644
--- a/src/parser/instruction.ts
+++ b/src/parser/instruction.ts
@@ -4,28 +4,32 @@ enum InstructionType
 {
     Point,
     Line,
-    Circle
+    Circle,
+    Length
 }
 
 abstract class Instruction 
 {
     public fn: InstructionType;
     public params :Parameter[];
+    private argc: number;
 
-    constructor(type: InstructionType)
+    constructor(type: InstructionType, argc: number)
     {
         this.fn = type;
+        this.argc = argc;
         this.params = [];
     }
 
     abstract eval();
+    public getParameterCount(): number { return this.argc; }
 }
 
 class PointInstruction extends Instruction
 {
     constructor()
     {
-        super(InstructionType.Point);
+        super(InstructionType.Point, 2);
     }
 
     eval()
@@ -38,7 +42,7 @@ class LineInstruction extends Instruction
 {
     constructor()
     {
-        super(InstructionType.Line);
+        super(InstructionType.Line, 2);
     }
 
     eval()
@@ -48,4 +52,36 @@ class LineInstruction extends Instruction
             this.params[1].eval()
         ];
     }
+}
+
+class CircleInstruction extends Instruction
+{
+    constructor()
+    {
+        super(InstructionType.Line, 2);
+    }
+
+    eval()
+    {
+        return [
+            this.params[0].eval(),
+            this.params[1].eval()
+        ];
+    }
+}
+
+class LengthInstruction extends Instruction
+{
+    constructor()
+    {
+        super(InstructionType.Line, 1);
+    }
+
+    eval()
+    {
+        let line = this.params[0].eval();
+        let dx = line[1].x - line[0].x;
+        let dy = line[1].y - line[0].y;
+        return Math.sqrt(Math.pow(dx, 2) + Math.pow(dy, 2));
+    }
 }
\ No newline at end of file
diff --git a/src/parser/parser.ts b/src/parser/parser.ts
index 2a74445..ee57532 100644
--- a/src/parser/parser.ts
+++ b/src/parser/parser.ts
@@ -15,8 +15,9 @@ class Parser
         for(let line of lines)
         {
             let instr = this.parseInstruction(line);
-            if(!instr[0])
-                this.instructions.push(instr[1]);
+            if(instr !== null)
+                if(!instr[0])
+                    this.instructions.push(instr[1]);  
         }
     }
 
@@ -80,6 +81,18 @@ class Parser
                 break;
             }
 
+            case "circle":
+            {
+                newInstruction = new CircleInstruction();
+                break;
+            }
+
+            case "len":
+            {
+                newInstruction = new LengthInstruction();
+                break;
+            }
+
             default:
             {
                 console.error("Unknown instruction \"" + symbol + "\"");
@@ -87,6 +100,13 @@ class Parser
             }
         }
 
+        let expectedArgs = newInstruction.getParameterCount();
+        if(expectedArgs !== params.length)
+        {
+            console.error("Wrong number of arguments for instruction \"" + symbol + "\". Expected " + expectedArgs + " arguments but received " + params.length + " instead.");
+            return null;
+        }
+
         for(let param of params)
         {
             if(!this.parseParameter(newInstruction, param))
@@ -100,7 +120,6 @@ class Parser
         if(assignment !== -1)
         {
             let variableName = instruction.substring(assignment + 2, instruction.length);
-
             if(variableName in this.variables)
             {
                 console.error("Redefinition of variable \"" + variableName + "\" is not allowed.");
@@ -115,7 +134,7 @@ class Parser
 
     private parseParameter(instr: Instruction, parameter: string): boolean
     {
-        let match = parameter.match(/\d*\.?\d*$/);
+        let match = parameter.match(/-?\d*\.?\d*$/);
         if(match !== null && match[0] === parameter && match.index === 0)
         {
             let val = parseFloat(parameter);
@@ -125,7 +144,7 @@ class Parser
             return true;
         }
 
-        match = parameter.match(/[A-Za-z]/)
+        match = parameter.match(/[A-Za-z]*/)
         if(match !== null && match[0] === parameter && match.index === 0)
         {
             let paramObj = this.variables[parameter];