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package main
import (
"fmt"
"strings"
"unicode/utf8"
)
type stateFunc func(*lexer) stateFunc
type lexer struct {
input string
start int
pos int
width int
tokenStream chan Token
}
func (l *lexer) run() {
for state := lexCommand; state != nil; {
state = state(l)
}
close(l.tokenStream)
}
func (l *lexer) emit(t TokenType) {
l.tokenStream <- Token{
typ: t,
val: l.input[l.start:l.pos],
}
l.start = l.pos
}
func (l *lexer) errorf(format string, args ...interface{}) stateFunc {
l.tokenStream <- Token{
typ: TokenErr,
val: fmt.Sprintf(format, args...),
}
return nil
}
const eof rune = -1
func (l *lexer) next() rune {
if l.pos >= len(l.input) {
l.width = 0
return eof
}
var r rune
r, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
l.pos += l.width
return r
}
func (l *lexer) backup() {
l.pos -= l.width
}
func (l *lexer) ignore() {
l.start = l.pos
}
func (l *lexer) reset() {
l.pos = l.start
}
func (l *lexer) expect(valid string) bool {
for _, r := range valid {
if l.next() != r {
l.backup()
return false
}
}
return true
}
func (l *lexer) peek() rune {
w := l.width
r := l.next()
l.backup()
l.width = w
return r
}
func (l *lexer) accept(valid string) bool {
if strings.IndexRune(valid, l.next()) >= 0 {
return true
}
l.backup()
return false
}
func (l *lexer) acceptAll(valid string) {
for strings.IndexRune(valid, l.next()) >= 0 {}
l.backup()
}
func (l *lexer) acceptPassing(valid func(rune) bool) bool {
if valid(l.next()) {
return true
}
l.backup()
return false
}
func (l *lexer) acceptAllPassing(valid func(rune) bool) {
for valid(l.next()) {}
l.backup()
}
type TokenType int
const (
TokenErr TokenType = iota // Lexing error
TokenEOF // end of file
TokenLBrace // {
TokenRBrace // }
TokenCommand // A command character
TokenSubstituteDelimiter // usually / but could be something else
TokenSubex // A subex
TokenLabel // A label
)
type Token struct {
typ TokenType
val string
}
func (t Token) String() string {
switch t.typ {
case TokenEOF:
return "EOF"
case TokenErr:
return t.val
}
if len(t.val) > 10 {
return fmt.Sprintf("%.10q...", t.val)
}
return fmt.Sprintf("%q", t.val)
}
func Lex(input string) chan Token {
l := &lexer{
input: input,
tokenStream: make(chan Token),
}
go l.run()
return l.tokenStream
}
const (
whitespace string = " \t"
whitespaceNewlines string = " \t\r\n"
)
func isAlpha(r rune) bool {
return ('a' <= r && r < 'z') || ('A' <= r && r <= 'Z')
}
func isDigit(r rune) bool {
return '0' <= r && r <= '9'
}
func isAlphaNumeric(r rune) bool {
return isAlpha(r) || isDigit(r)
}
func isStringIndexChar(r rune) bool {
return isAlphaNumeric(r) || r == '_' || r == '-'
}
func lexCommand(l *lexer) stateFunc {
l.acceptAll(whitespace)
l.ignore()
r := l.next()
switch r {
case eof:
l.emit(TokenEOF)
return nil
case '{':
l.emit(TokenLBrace)
return lexCommand
case '}':
l.emit(TokenRBrace)
return lexCommand
case 's', 'S':
l.emit(TokenCommand)
return lexSubstitution
case 'x', 'X', 'y', 'Y', 'z', 'Z', 'n', 'N':
l.emit(TokenCommand)
if l.peek() == '/' {
return lexSubstitution
} else {
return lexCommand
}
case ':', 'b':
l.emit(TokenCommand)
return lexLabel
}
if isAlpha(r) {
l.emit(TokenCommand)
return lexCommand
}
return l.errorf("Expected command found something else")
}
func lexSubstitution(l *lexer) stateFunc {
delimiter := l.next()
if delimiter == eof {
return l.errorf("Missing subex in substitution command")
}
l.emit(TokenSubstituteDelimiter)
loop: for {
r := l.next()
switch r {
case delimiter:
l.backup()
l.emit(TokenSubex)
l.next()
l.emit(TokenSubstituteDelimiter)
break loop
case eof:
return l.errorf("Missing closing substitution delimiter")
default:
}
}
return lexCommand
}
func lexLabel(l *lexer) stateFunc {
l.next()
l.emit(TokenLabel)
return lexCommand
}
|
