### 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

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

// 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",