Solution proposal for #181

json-path/src/main/java/com/jayway/jsonpath/internal/filter/EvaluatorFactory.java

@@ -240,13 +240,28 @@ public class EvaluatorFactory {
             if(!(left.isPatternNode() ^ right.isPatternNode())){
                 return false;
             }
-            if(!(left.isStringNode() ^ right.isStringNode())){
+
-                return false;
+            if (left.isPatternNode()) {
+                return matches(left.asPatternNode(), getInput(right));
+            } else {
+                return matches(right.asPatternNode(), getInput(left));
+            }
+        }
+
+        private boolean matches(ValueNode.PatternNode patternNode, String inputToMatch) {
+            return patternNode.getCompiledPattern().matcher(inputToMatch).matches();
+        }
+
+        private String getInput(ValueNode valueNode) {
+            String input = "";
+
+            if (valueNode.isStringNode() || valueNode.isNumberNode()) {
+                input = valueNode.asStringNode().getString();
+            } else if (valueNode.isBooleanNode()) {
+                input = valueNode.asBooleanNode().toString();
             }
-            ValueNode.PatternNode patternNode = left.isPatternNode() ? left.asPatternNode() : right.asPatternNode();
-            ValueNode.StringNode stringNode = left.isStringNode() ? left.asStringNode() : right.asStringNode();
 
-            return patternNode.getCompiledPattern().matcher(stringNode.getString()).matches();
+            return input;
         }
     }
 }

json-path/src/test/java/com/jayway/jsonpath/internal/filter/RegexpEvaluatorTest.java

@@ -0,0 +1,76 @@
+package com.jayway.jsonpath.internal.filter;
+
+import com.jayway.jsonpath.BaseTest;
+import com.jayway.jsonpath.Predicate;
+import com.jayway.jsonpath.internal.Path;
+import com.jayway.jsonpath.internal.path.CompiledPath;
+import com.jayway.jsonpath.internal.path.PathTokenFactory;
+import org.assertj.core.util.Maps;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+
+import java.util.Arrays;
+
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
+
+import static com.jayway.jsonpath.internal.filter.ValueNode.*;
+
+@RunWith(Parameterized.class)
+public class RegexpEvaluatorTest extends BaseTest {
+
+    private String regexp;
+    private ValueNode valueNode;
+    private boolean expectedResult;
+
+    public RegexpEvaluatorTest(String regexp, ValueNode valueNode, boolean expectedResult) {
+        this.regexp = regexp;
+        this.valueNode = valueNode;
+        this.expectedResult = expectedResult;
+    }
+
+    @Test
+    public void should_evaluate_regular_expression() {
+        //given
+        Evaluator evaluator = EvaluatorFactory.createEvaluator(RelationalOperator.REGEX);
+        ValueNode patternNode = createPatternNode(regexp);
+        Predicate.PredicateContext ctx = createPredicateContext();
+
+        //when
+        boolean result = evaluator.evaluate(patternNode, valueNode, ctx);
+
+        //then
+        assertThat(result, is(equalTo(expectedResult)));
+    }
+
+    @Parameterized.Parameters(name="Regexp {0} for {1} node should evaluate to {2}")
+    public static Iterable data() {
+        return Arrays.asList(
+            new Object[][]{
+                { "/true|false/", createStringNode("true", true),   true  },
+                { "/9.*9/",       createNumberNode("9979"),         true  },
+                { "/fa.*se/",     createBooleanNode("false"),       true  },
+                { "/Eval.*or/",   createClassNode(String.class),    false },
+                { "/JsonNode/",   createJsonNode(json()),           false },
+                { "/PathNode/",   createPathNode(path()),           false },
+                { "/Undefined/",  createUndefinedNode(),            false },
+                { "/NullNode/",   createNullNode(),                 false }
+            }
+        );
+    }
+
+    private static Path path() {
+        return new CompiledPath(PathTokenFactory.createRootPathToken('$'), true);
+    }
+
+    private static String json() {
+        return "{ 'some': 'JsonNode' }";
+    }
+
+    private Predicate.PredicateContext createPredicateContext() {
+        return createPredicateContext(Maps.newHashMap());
+    }
+
+}