Moved register state to scopes

src/build/expression/Expression.go

@@ -32,6 +32,21 @@ func (expr *Expression) AddChild(child *Expression) {
 	child.Parent = expr
 }
 
+// Count counts how often the given token appears in the expression.
+func (expr *Expression) Count(kind token.Kind, name string) int {
+	count := 0
+
+	expr.EachLeaf(func(leaf *Expression) error {
+		if leaf.Token.Kind == kind && leaf.Token.Text() == name {
+			count++
+		}
+
+		return nil
+	})
+
+	return count
+}
+
 // Reset resets all values to the default.
 func (expr *Expression) Reset() {
 	for _, child := range expr.Children {

src/build/expression/Expression_test.go

@@ -9,7 +9,7 @@ import (
 	"git.akyoto.dev/go/assert"
 )
 
-func TestExpressionParse(t *testing.T) {
+func TestParse(t *testing.T) {
 	tests := []struct {
 		Name       string
 		Expression string
@@ -96,6 +96,17 @@ func TestExpressionParse(t *testing.T) {
 	}
 }
 
+func TestCount(t *testing.T) {
+	src := []byte("(a+b-c*d)+(a*b-c+d)")
+	tokens := token.Tokenize(src)
+	expr := expression.Parse(tokens)
+	assert.Equal(t, expr.Count(token.Identifier, "a"), 2)
+	assert.Equal(t, expr.Count(token.Identifier, "b"), 2)
+	assert.Equal(t, expr.Count(token.Identifier, "c"), 2)
+	assert.Equal(t, expr.Count(token.Identifier, "d"), 2)
+	assert.Equal(t, expr.Count(token.Identifier, "e"), 0)
+}
+
 func TestEachLeaf(t *testing.T) {
 	src := []byte("(1+2-3*4)+(5*6-7+8)")
 	tokens := token.Tokenize(src)