diff --git a/sources/zweic/Analyzer.scala b/sources/zweic/Analyzer.scala
index 6c9eb91..6826852 100755
--- a/sources/zweic/Analyzer.scala
+++ b/sources/zweic/Analyzer.scala
@@ -75,6 +75,9 @@
 		case MethodDef(name, args, rtype, expr) =>
 			var myVarScope = emptyVarScope;
 
+			//XXX
+			tree.asInstanceOf[MethodDef].self = Name(ownerClass.name);
+
 			myVarScope = myVarScope + "this" -> VarSymbol(ownerClass.pos, "this", IClassType(ownerClass));
 
 			val paramtypes = for ( val f <- args ) yield {
diff --git a/sources/zweic/Generator.scala b/sources/zweic/Generator.scala
index a033e9d..9643026 100644
--- a/sources/zweic/Generator.scala
+++ b/sources/zweic/Generator.scala
@@ -48,14 +48,14 @@
 		}
 	}
 
+      // generate class and function definitions
+	classes.foreach(gen);
+
 	genTmp { tmpReg =>
 		emitLoadConstant(tmpReg, offset);
 		code.emit(SYSCALL, tmpReg, tmpReg, SYS_GC_ALLOC);
 	}
 
-      // generate class and function definitions
-	classes.foreach(gen);
-
       // generate main expression
       val start = code.getLabel();
       code.anchorLabel(start);
@@ -278,9 +278,9 @@
 
       case Ident(name) =>
 		if ( name.name == "this" ) {
-			code.emit(LDW, targetReg, SP, code.getFrameSize());
+			code.emit(LDW, targetReg, SP, code.getFrameSize(), name.name);
 		} else {
-			code.emit(LDW, targetReg, SP, code.getFrameSize()-(name.sym.offset));
+			code.emit(LDW, targetReg, SP, code.getFrameSize()-(name.sym.offset), name.name);
 		}
 
       case New(name, args) =>
@@ -301,57 +301,77 @@
 	}
 
       case Select(prefix, selector) =>
-	genTmp { tmpReg =>
-		genLoad(prefix, tmpReg);
-		// TODO check tmpReg != null
-		code.emit(LDW, targetReg, tmpReg, selector.sym.offset+4);
-	}
+	genLoad(prefix, targetReg);
 
-      case Call(receiver, method, args) =>		
-		genTmp { thisReg =>
+	val okLabel = code.getLabel();
 
-			// put all registers on stack
-			val used = code.usedRegisters();
+	// check prefix != null
+	code.emit(BNE, targetReg, okLabel);
+	emitLoadConstant(targetReg, 1);
+	code.emit(SYSCALL, targetReg, ZERO, SYS_EXIT);
 
-			for ( val i <- Iterator.range(0, used.length)) {
-				if ( used(i) && i != targetReg ) {
-					code.emit(PSH, i, SP, 4);
-					code.incFrameSize(4);
-				}
+	code.anchorLabel(okLabel);
+
+	code.emit(LDW, targetReg, targetReg, selector.sym.offset+4);
+
+      case Call(receiver, method, args) =>
+		
+		// put all registers on stack
+		val used = code.usedRegisters();
+		var freed:List[Int] = Nil;
+
+		for ( val i <- Iterator.range(0, used.length)) {
+			if ( used(i) && i != targetReg ) {
+				code.emit(PSH, i, SP, 4);
+				code.incFrameSize(4);
+				code.freeRegister(i);
+				freed = i::freed;
 			}
-			
-			// get 'this' and put it on stack
-			genLoad(receiver, thisReg);
-			code.emit(PSH, thisReg, SP, 4);
-			code.incFrameSize(4);
-			
-			// put args on stack
-			genTmp { tmpReg =>
-				for ( val a <- args ) {
-					genLoad(a, tmpReg);
-					code.emit(PSH, tmpReg, SP, 4);
-					code.incFrameSize(4);
-				}
+		}
+		
+		// get 'receiver' and put it as 'this' on the stack
+		genLoad(receiver, targetReg);
+
+		// check receiver != null
+		val okLabel = code.getLabel();
+		code.emit(BNE, targetReg, okLabel);
+		emitLoadConstant(targetReg, 1);
+		code.emit(SYSCALL, targetReg, ZERO, SYS_EXIT);
+		code.anchorLabel(okLabel);
+
+		code.emit(PSH, targetReg, SP, 4);
+		code.incFrameSize(4);
+		
+		// put args on stack
+		genTmp { tmpReg =>
+			for ( val a <- args ) {
+				genLoad(a, tmpReg);
+				code.emit(PSH, tmpReg, SP, 4);
+				code.incFrameSize(4);
 			}
+		}
 
-			//TODO check thisReg != null
-			code.emit(LDW, thisReg, thisReg, method.sym.offset);
-			//TODO check thisReg != null
+		code.emit(LDW, targetReg, targetReg, method.sym.offset);
 
-			code.emit(RET, thisReg);
+		// check receiver.method() != null
+		val okLabel2 = code.getLabel();
+		code.emit(BNE, targetReg, okLabel2);
+		emitLoadConstant(targetReg, 1);
+		code.emit(SYSCALL, targetReg, ZERO, SYS_EXIT);
+		code.anchorLabel(okLabel2);
+
+		code.emit(RET, targetReg);
 
 
-			code.emit(ADD, targetReg, ZERO, RES);
+		code.emit(ADD, targetReg, ZERO, RES);
 
-			code.decFrameSize(args.length*4+4); // fs = oldframesize - params - this
-			
-			// retrieve all registers from stack
-			for ( val j <- Iterator.range(0, used.length)) {
-				if ( used(j) && j != targetReg ) {
-					code.emit(POP, j, SP, 4);
-					code.decFrameSize(4);
-				}
-			}
+		code.decFrameSize(args.length*4+4); // fs = oldframesize - params - this
+		
+		// retrieve all registers from stack
+		for ( val j <- freed ) {
+			code.getRegister(j);
+			code.emit(POP, j, SP, 4);
+			code.decFrameSize(4);
 		}
 
       case If(cond, thenp, elsep) =>
@@ -385,6 +405,7 @@
 				genLoad(left, tmpLeft);
 				genLoad(right, tmpRight);
 			op match {
+				// TODO do all this with CMP !!!
 				case Operators.EQ =>
 					code.emit(CMP, tmpLeft, tmpLeft, tmpRight, "");
 					if ( when ) {
@@ -410,7 +431,7 @@
 					}
 
 				case Operators.SUB =>
-					code.emit(SUB, tmpLeft, tmpLeft, tmpRight);
+					code.emit(CMP, tmpLeft, tmpLeft, tmpRight);
 					if ( when ) {
 						code.emit(BNE, tmpLeft, targetLabel);
 					} else {
@@ -442,7 +463,7 @@
 					}
 
 				case Operators.LT =>
-					code.emit(SUB, tmpLeft, tmpLeft, tmpRight);
+					code.emit(CMP, tmpLeft, tmpLeft, tmpRight);
 					if ( when ) {
 						code.emit(BLT, tmpLeft, targetLabel);
 					} else {
@@ -450,7 +471,7 @@
 					}
 
 				case Operators.LE =>
-					code.emit(SUB, tmpLeft, tmpLeft, tmpRight);
+					code.emit(CMP, tmpLeft, tmpLeft, tmpRight);
 					if ( when ) {
 						code.emit(BLE, tmpLeft, targetLabel);
 					} else {
@@ -458,7 +479,7 @@
 					}
 
 				case Operators.GT =>
-					code.emit(SUB, tmpLeft, tmpLeft, tmpRight);
+					code.emit(CMP, tmpLeft, tmpLeft, tmpRight);
 					if ( when ) {
 						code.emit(BGT, tmpLeft, targetLabel);
 					} else {
@@ -466,7 +487,7 @@
 					}
 
 				case Operators.GE =>
-					code.emit(SUB, tmpLeft, tmpLeft, tmpRight);
+					code.emit(CMP, tmpLeft, tmpLeft, tmpRight);
 					if ( when ) {
 						code.emit(BGE, tmpLeft, targetLabel);
 					} else {
diff --git a/sources/zweic/Tree.scala b/sources/zweic/Tree.scala
index cb83d99..f997a92 100755
--- a/sources/zweic/Tree.scala
+++ b/sources/zweic/Tree.scala
@@ -54,7 +54,7 @@
 case class MethodDef(name: Name, args: List[Formal],
 		     returntype: TypeTree, expression: Expr)
      extends Member {
-  val self: Name = Name("this");
+  var self: Name = Name("this");
 }
 
 /* F = Formal name T */