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+ The PR title is formatted as follows: `net/http: frob the quux before blarfing`
  + The package name goes before the colon

	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()
}

### Iterators

The new [`iter` package](/pkg/iter/) provides the basic definitions for

pkg iter, func Pull2[$0 interface{}, $1 interface{}](Seq2[$0, $1]) (func() ($0, $1, bool), func()) #61897
pkg iter, func Pull[$0 interface{}](Seq[$0]) (func() ($0, bool), func()) #61897
pkg iter, type Seq2[$0 interface{}, $1 interface{}] func(func($0, $1) bool) #61897

// Package lex implements lexical analysis for the assembler.
package lex

import (
	"fmt"
	"log"
	"os"
	"strings"
	"text/scanner"

	"cmd/internal/src"
)

// A ScanToken represents an input item. It is a simple wrapping of rune, as
// returned by text/scanner.Scanner, plus a couple of extra values.
type ScanToken rune

const (
	// Asm defines some two-character lexemes. We make up

		}
		buf.WriteString(input.Text())
	}
}

type badLexTest struct {
	input string
	error string
}

var badLexTests = []badLexTest{
	{
		"3 #define foo bar\n",
		"'#' must be first item on line",
	},
	{
		"#ifdef foo\nhello",
		"unclosed #ifdef or #ifndef",
	},
	{
		"#ifndef foo\nhello",
		"unclosed #ifdef or #ifndef",
	},
	{
		"#ifdef foo\nhello\n#else\nbye",

<!-- see ../../3-iter.md -->...