Improved expression parser

src/build/expression/Expression.go

@@ -8,9 +8,10 @@ import (
 
 // Expression is a binary tree with an operator on each node.
 type Expression struct {
-	Token    token.Token
-	Parent   *Expression
-	Children []*Expression
+	Token      token.Token
+	Parent     *Expression
+	Children   []*Expression
+	Precedence int
 }
 
 // New creates a new expression.
@@ -49,6 +50,7 @@ func (expr *Expression) Close() {
 	expr.Token.Reset()
 	expr.Parent = nil
 	expr.Children = expr.Children[:0]
+	expr.Precedence = 0
 	pool.Put(expr)
 }