Add functional value

app/src/main/java/com/annimon/hotarufx/lib/FunctionValue.java

@@ -0,0 +1,69 @@
+package com.annimon.hotarufx.lib;
+
+import com.annimon.hotarufx.exceptions.TypeException;
+import java.util.Objects;
+import lombok.Getter;
+
+public class FunctionValue implements Value {
+
+    public static final FunctionValue EMPTY = new FunctionValue(args -> NumberValue.ZERO);
+
+    @Getter
+    private final Function value;
+
+    public FunctionValue(Function value) {
+        this.value = value;
+    }
+
+    @Override
+    public int type() {
+        return Types.FUNCTION;
+    }
+
+    @Override
+    public Object raw() {
+        return value;
+    }
+
+    @Override
+    public int asInt() {
+        throw new TypeException("Cannot cast function to integer");
+    }
+
+    @Override
+    public double asNumber() {
+        throw new TypeException("Cannot cast function to number");
+    }
+
+    @Override
+    public String asString() {
+        return value.toString();
+    }
+
+    @Override
+    public int hashCode() {
+        int hash = 7;
+        hash = 71 * hash + Objects.hashCode(this.value);
+        return hash;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) return true;
+        if (obj == null) return false;
+        if (getClass() != obj.getClass())
+            return false;
+        final FunctionValue other = (FunctionValue) obj;
+        return Objects.equals(this.value, other.value);
+    }
+
+    @Override
+    public int compareTo(Value o) {
+        return asString().compareTo(o.asString());
+    }
+
+    @Override
+    public String toString() {
+        return asString();
+    }
+}

app/src/main/java/com/annimon/hotarufx/lib/Types.java

@@ -8,5 +8,6 @@ public class Types {
             STRING = 2,
             MAP = 3,
             NODE = 4,
-            FUNCTION = 5;
+            PROPERTY = 5,
+            FUNCTION = 6;
 }