Enable comparison feature like python

ast/node.go

@@ -234,3 +234,11 @@ type PairNode struct {
 	Key   Node // Key of the pair.
 	Value Node // Value of the pair.
 }
+
+// CompareNode represents comparison
+type CompareNode struct {
+	base
+	Left        Node     // Left represents the left-hand side of the comparison operation
+	Operators   []string // Operators is a list of comparison operator tokens used in the comparison.
+	Comparators []Node   // Comparators representing the right-hand sides of the comparison operation
+}

ast/print.go

@@ -219,3 +219,34 @@ func (n *PairNode) String() string {
 	}
 	return fmt.Sprintf("(%s): %s", n.Key.String(), n.Value.String())
 }
+
+func (n *CompareNode) string(node Node) string {
+	switch v := node.(type) {
+	case *BinaryNode, *CompareNode:
+		return fmt.Sprintf("(%s)", v)
+	default:
+		return v.String()
+	}
+}
+
+func (n *CompareNode) String() string {
+	var builder strings.Builder
+	builder.WriteString(n.string(n.Left))
+	opIdx := 0
+	for i := 0; i < len(n.Comparators); i++ {
+		if op := n.Operators[opIdx]; op != "&&" {
+			builder.WriteByte(' ')
+			builder.WriteString(op)
+			if op == "not" {
+				opIdx++
+				builder.WriteByte(' ')
+				builder.WriteString(n.Operators[opIdx])
+			}
+			builder.WriteByte(' ')
+			builder.WriteString(n.string(n.Comparators[i]))
+		}
+		opIdx++
+	}
+
+	return builder.String()
+}

ast/print_test.go

@@ -41,7 +41,7 @@ func TestPrint(t *testing.T) {
 		{`a == b`, `a == b`},
 		{`a matches b`, `a matches b`},
 		{`a in b`, `a in b`},
-		{`a not in b`, `not (a in b)`},
+		{`a not in b`, `a not in b`},
 		{`a and b`, `a and b`},
 		{`a or b`, `a or b`},
 		{`a or b and c`, `a or (b and c)`},

ast/visitor.go

@@ -66,6 +66,11 @@ func Walk(node *Node, v Visitor) {
 	case *PairNode:
 		Walk(&n.Key, v)
 		Walk(&n.Value, v)
+	case *CompareNode:
+		Walk(&n.Left, v)
+		for i := range n.Comparators {
+			Walk(&n.Comparators[i], v)
+		}
 	default:
 		panic(fmt.Sprintf("undefined node type (%T)", node))
 	}

checker/checker.go

@@ -166,6 +166,8 @@ func (v *checker) visit(node ast.Node) Nature {
 		nt = v.MapNode(n)
 	case *ast.PairNode:
 		nt = v.PairNode(n)
+	case *ast.CompareNode:
+		nt = v.CompareNode(n)
 	default:
 		panic(fmt.Sprintf("undefined node type (%T)", node))
 	}
@@ -282,11 +284,6 @@ func (v *checker) BinaryNode(node *ast.BinaryNode) Nature {
 	r = r.Deref()
 
 	switch node.Operator {
-	case "==", "!=":
-		if isComparable(l, r) {
-			return boolNature
-		}
-
 	case "or", "||", "and", "&&":
 		if isBool(l) && isBool(r) {
 			return boolNature
@@ -295,20 +292,6 @@ func (v *checker) BinaryNode(node *ast.BinaryNode) Nature {
 			return boolNature
 		}
 
-	case "<", ">", ">=", "<=":
-		if isNumber(l) && isNumber(r) {
-			return boolNature
-		}
-		if isString(l) && isString(r) {
-			return boolNature
-		}
-		if isTime(l) && isTime(r) {
-			return boolNature
-		}
-		if or(l, r, isNumber, isString, isTime) {
-			return boolNature
-		}
-
 	case "-":
 		if isNumber(l) && isNumber(r) {
 			return combined(l, r)
@@ -372,51 +355,6 @@ func (v *checker) BinaryNode(node *ast.BinaryNode) Nature {
 			return unknown
 		}
 
-	case "in":
-		if (isString(l) || isUnknown(l)) && isStruct(r) {
-			return boolNature
-		}
-		if isMap(r) {
-			if !isUnknown(l) && !l.AssignableTo(r.Key()) {
-				return v.error(node, "cannot use %v as type %v in map key", l, r.Key())
-			}
-			return boolNature
-		}
-		if isArray(r) {
-			if !isComparable(l, r.Elem()) {
-				return v.error(node, "cannot use %v as type %v in array", l, r.Elem())
-			}
-			return boolNature
-		}
-		if isUnknown(l) && anyOf(r, isString, isArray, isMap) {
-			return boolNature
-		}
-		if isUnknown(r) {
-			return boolNature
-		}
-
-	case "matches":
-		if s, ok := node.Right.(*ast.StringNode); ok {
-			_, err := regexp.Compile(s.Value)
-			if err != nil {
-				return v.error(node, err.Error())
-			}
-		}
-		if isString(l) && isString(r) {
-			return boolNature
-		}
-		if or(l, r, isString) {
-			return boolNature
-		}
-
-	case "contains", "startsWith", "endsWith":
-		if isString(l) && isString(r) {
-			return boolNature
-		}
-		if or(l, r, isString) {
-			return boolNature
-		}
-
 	case "..":
 		if isInteger(l) && isInteger(r) {
 			return Nature{
@@ -1230,3 +1168,87 @@ func (v *checker) PairNode(node *ast.PairNode) Nature {
 	v.visit(node.Value)
 	return nilNature
 }
+
+func (v *checker) CompareNode(node *ast.CompareNode) Nature {
+	nodeLeft := node.Left
+	opIdx := 0
+	operatorOverride := false
+	for i, comparator := range node.Comparators {
+		op := node.Operators[opIdx]
+		if negate := op == "not"; negate {
+			opIdx++
+			op = node.Operators[opIdx]
+		}
+		if op == "&&" {
+			if !operatorOverride {
+				operatorOverride = true
+			}
+		} else if err := v.compareNode(op, nodeLeft, comparator, i); err != nil {
+			return v.error(comparator, err.Error())
+		}
+		opIdx++
+		nodeLeft = comparator
+	}
+	if operatorOverride {
+		return unknown
+	}
+	return boolNature
+}
+
+func (v *checker) compareNode(op string, nodeLeft, nodeRight ast.Node, index int) error {
+	l := v.visit(nodeLeft)
+	r := v.visit(nodeRight)
+
+	l = l.Deref()
+	r = r.Deref()
+	switch op {
+	case "==", "!=":
+		if (isBool(r) && index > 0) || isComparable(l, r) {
+			return nil
+		}
+	case "<", ">", ">=", "<=":
+		if isNumber(l) && isNumber(r) ||
+			isString(l) && isString(r) ||
+			isTime(l) && isTime(r) ||
+			or(l, r, isNumber, isString, isTime) {
+			return nil
+		}
+	case "in":
+		if (isString(l) || isUnknown(l)) && isStruct(r) {
+			return nil
+		}
+		if isMap(r) {
+			if !isUnknown(l) && !l.AssignableTo(r.Key()) {
+				return fmt.Errorf("cannot use %v as type %v in map key", l, r.Key())
+			}
+			return nil
+		}
+		if isArray(r) {
+			if !isComparable(l, r.Elem()) {
+				return fmt.Errorf("cannot use %v as type %v in array", l, r.Elem())
+			}
+			return nil
+		}
+		if (isUnknown(l) && anyOf(r, isString, isArray, isMap)) || isUnknown(r) {
+			return nil
+		}
+
+	case "matches":
+		if s, ok := nodeRight.(*ast.StringNode); ok {
+			if _, err := regexp.Compile(s.Value); err != nil {
+				return err
+			}
+		}
+		if (isString(l) && isString(r)) || or(l, r, isString) {
+			return nil
+		}
+	case "contains", "startsWith", "endsWith":
+		if isString(l) && isString(r) ||
+			or(l, r, isString) {
+			return nil
+		}
+	default:
+		return fmt.Errorf("unknown operator (%v)", op)
+	}
+	return fmt.Errorf(`invalid operation: %v (mismatched types %v and %v)`, op, l, r)
+}