added implementation of negative number matching.

src/org/rascalmpl/interpreter/matching/NegativePattern.java

@@ -20,7 +20,10 @@
 import org.rascalmpl.interpreter.IEvaluatorContext;
 import org.rascalmpl.interpreter.env.Environment;
 import org.rascalmpl.interpreter.result.Result;
+import org.rascalmpl.values.IRascalValueFactory;
+
 import io.usethesource.vallang.IValue;
+import io.usethesource.vallang.INumber;
 import io.usethesource.vallang.type.Type;
 
 public class NegativePattern extends AbstractMatchingResult {
@@ -43,7 +46,7 @@
 
 	@Override
 	public boolean mayMatch(Type subjectType, Environment env){
-		return pat.mayMatch(subjectType, env);
+		return subjectType.isSubtypeOf(tf.numberType()) && pat.mayMatch(subjectType, env);
 	}
 
 	@Override
@@ -53,6 +56,11 @@
 
 	@Override
 	public boolean next() {
-		return pat.next();
+		if (pat.next()) {
+			if (subject.getDynamicType().isNumber()) {
+				return ((INumber) subject.getValue()).lessEqual(IRascalValueFactory.getInstance().integer(0)).getValue();
+			}
+		}
+		return false;
 	}
 }

src/org/rascalmpl/semantics/dynamic/Expression.java

@@ -1918,8 +1918,15 @@
 		}
 
 		@Override
+		@SuppressWarnings("unchecked")
 		public IMatchingResult buildMatcher(IEvaluatorContext __eval, boolean bindTypeParameters) {
-			return new NegativePattern(__eval, this, getArgument().buildMatcher(__eval, bindTypeParameters));
+			Type t = getArgument().typeOf(__eval.getCurrentEnvt(), (IEvaluator<Result<IValue>>) __eval, bindTypeParameters);
+
+			if (getArgument().isTypedVariable() || getArgument().isQualifiedName() || getArgument().isLiteral()) {
+				return new NegativePattern(__eval, this, getArgument().buildMatcher(__eval, bindTypeParameters));				
+			}
+
+			throw new UnexpectedType(TF.numberType(), t, getLocation());
 		}
 
 		@Override