1 files changed, 61 insertions, 0 deletions
diff --git a/src/cmd/asm/internal/lex/stack.go b/src/cmd/asm/internal/lex/stack.go
new file mode 100644
index 0000000..929e528
--- /dev/null
+++ b/src/cmd/asm/internal/lex/stack.go
@@ -0,0 +1,61 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package lex
+
+import (
+	"text/scanner"
+
+	"cmd/internal/src"
+)
+
+// A Stack is a stack of TokenReaders. As the top TokenReader hits EOF,
+// it resumes reading the next one down.
+type Stack struct {
+	tr []TokenReader
+}
+
+// Push adds tr to the top (end) of the input stack. (Popping happens automatically.)
+func (s *Stack) Push(tr TokenReader) {
+	s.tr = append(s.tr, tr)
+}
+
+func (s *Stack) Next() ScanToken {
+	tos := s.tr[len(s.tr)-1]
+	tok := tos.Next()
+	for tok == scanner.EOF && len(s.tr) > 1 {
+		tos.Close()
+		// Pop the topmost item from the stack and resume with the next one down.
+		s.tr = s.tr[:len(s.tr)-1]
+		tok = s.Next()
+	}
+	return tok
+}
+
+func (s *Stack) Text() string {
+	return s.tr[len(s.tr)-1].Text()
+}
+
+func (s *Stack) File() string {
+	return s.Base().Filename()
+}
+
+func (s *Stack) Base() *src.PosBase {
+	return s.tr[len(s.tr)-1].Base()
+}
+
+func (s *Stack) SetBase(base *src.PosBase) {
+	s.tr[len(s.tr)-1].SetBase(base)
+}
+
+func (s *Stack) Line() int {
+	return s.tr[len(s.tr)-1].Line()
+}
+
+func (s *Stack) Col() int {
+	return s.tr[len(s.tr)-1].Col()
+}
+
+func (s *Stack) Close() { // Unused.
+}