     }
 
     /// The left operand of the expression.
-    public let left : Node
+    public var left : Node
 
     /// The operator of the expression.
-    public let op: Operator
+    public var op: Operator
 
     /// The right operand of the expression.
-    public let right: Node
+    public var right: Node
 
     // MARK: Annotations
 

    }

    /// The value of the literal.
    public let value: T

    // MARK: Annotations

    public var type    : SemanticType?
    public let location: SourceRange?

}

    }

    /// The callee.
    public var callee: Node

    /// The arguments of the call.
    public var arguments: [CallArg]

    // MARK: Annotations

