diff --git a/src/main/antlr/grammar/crml.g4 b/src/main/antlr/grammar/crml.g4
index 497f3213..ccee9505 100644
--- a/src/main/antlr/grammar/crml.g4
+++ b/src/main/antlr/grammar/crml.g4
@@ -93,7 +93,7 @@ if_exp : 'if' if_e=exp 'then' then_e=exp ('else' else_e=exp);
 
 constructor : 'new' type exp;
 	
-period_op : ('['| ']') exp ',' exp ('['| ']') ; 
+period_op : lb=('['| ']') exp ',' exp rb=('['| ']') ; 
 
 op : builtin_op|user_keyword
 ;
diff --git a/src/main/java/crml/compiler/crmlVisitorImpl.java b/src/main/java/crml/compiler/crmlVisitorImpl.java
index 101efcc0..db1e98d4 100644
--- a/src/main/java/crml/compiler/crmlVisitorImpl.java
+++ b/src/main/java/crml/compiler/crmlVisitorImpl.java
@@ -490,7 +490,9 @@ else if (ctx.uninstantiated_def()!=null)
 			if(ctx.sub_exp()!=null)
 				return visit(ctx.sub_exp().exp());
 		
-
+			if(ctx.period_op()!=null){
+				return visit(ctx.period_op());
+			}
 			
 			// expression is a tick
 			if(ctx.tick() != null) {
@@ -530,10 +532,32 @@ private UserOperatorCall reconstructUserOperator(ExpContext ctx, String string,
 		}
 
 	@Override
-	public Value visitSet_def(crmlParser.Set_defContext cxt) {
+	public Value visitSet_def(crmlParser.Set_defContext ctx) {
 		return new Value ("Set", "{}", true);
 	}
 
+	@Override
+	public Value visitPeriod_op(crmlParser.Period_opContext ctx) {
+		
+		//String periodType = types_mapping.get("Period");
+
+		//TODO add typechecking
+		
+		Value left = visit(ctx.exp(0));
+		Value right = visit(ctx.exp(0));
+
+		Boolean lborder = (ctx.lb.getText().equals("["));
+		Boolean rborder = (ctx.rb.getText().equals("]"));
+
+		String code = 
+			"CRMLtoModelica.Types.CRMLPeriod(left=" + left.contents + 
+		    ", right=" + right.contents + 
+			",lb=" +lborder.toString() + 
+			",rb=" +rborder.toString()+");";
+			
+		return new Value (code, "Period", false);
+	}
+
 	@Override
 	public Value visitId(crmlParser.IdContext ctx){
 		VariableData.VariableType v_type = variableTable.getVariableInfo(ctx.getText());