ExpressionConstant.evaluate(): cast BigRational constants to type

If we evaluate() a BigRational constant, convert to corresponding Java data type (might lose precision)

prism/src/parser/ast/ExpressionConstant.java

@@ -82,6 +82,13 @@ public class ExpressionConstant extends Expression
 		Object res = ec.getConstantValue(name);
 		if (res == null)
 			throw new PrismLangException("Could not evaluate constant", this);
+
+		if (res instanceof BigRational) {
+			// Constants can also be BigRational, cast to appropriate type
+			// This might lose precision
+			BigRational r = (BigRational) res;
+			return getType().castFromBigRational(r);
+		}
 		return res;
 	}