1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
|
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', 'M':
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
}
|
