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lexer.go
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lexer.go
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package jsonexpr
import (
"bufio"
"fmt"
"io"
"strconv"
"text/scanner"
)
type Scanner struct {
buf *bufio.Reader
data []interface{}
err error
debug bool
}
func NewScanner(r io.Reader, debug bool) *Scanner {
return &Scanner{
buf: bufio.NewReader(r),
debug: debug,
}
}
func (sc *Scanner) Error(s string) {
sc.err = fmt.Errorf(s)
fmt.Printf("syntax error: %s\n", s)
}
func (sc *Scanner) Reduced(rule, state int, lval *JSONExprSymType) bool {
if sc.debug {
fmt.Printf("rule: %v; state %v; lval: %v\n", rule, state, lval)
}
return false
}
func (sc *Scanner) Lex(lval *JSONExprSymType) int {
return sc.lex(lval)
}
func (sc *Scanner) lex(lval *JSONExprSymType) int {
for {
r := sc.read()
if r == 0 {
return 0
}
if isWhitespace(r) {
continue
}
if isDigit(r) {
sc.unread()
val, err := sc.scanInt()
if err != nil {
sc.err = fmt.Errorf(err.Error())
return 0
}
lval.int = val
return INDEX
}
switch true {
case r == '[':
return LSB
case r == ']':
return RSB
case r == '.':
return DOT
case isIdentifier(r):
sc.unread()
lval.field = sc.scanField()
return FIELD
case r == '"':
sc.unread()
lval.str = sc.scanStr()
return STRING
default:
sc.err = fmt.Errorf("unexpected char %c", r)
return 0
}
}
}
func isIdentifier(r rune) bool {
return (r >= 'a' && r <= 'z') || (r >= 'A' && r <= 'Z') || r == '_'
}
func (sc *Scanner) scanField() string {
var str []rune
for {
r := sc.read()
if !isIdentifier(r) {
sc.unread()
break
}
if r == '.' || r == scanner.EOF || r == rune(0) {
sc.unread()
break
}
str = append(str, r)
}
return string(str)
}
func (sc *Scanner) scanStr() string {
var str []rune
//begin with ", end with "
r := sc.read()
if r != '"' {
sc.err = fmt.Errorf("unexpected char %c", r)
return ""
}
for {
r := sc.read()
if r == '"' || r == ']' {
break
}
str = append(str, r)
}
return string(str)
}
func (sc *Scanner) scanInt() (int, error) {
var number []rune
for {
r := sc.read()
if r == '.' && len(number) > 0 {
return 0, fmt.Errorf("cannot use float as array index")
}
if isWhitespace(r) || r == '.' || r == ']' {
sc.unread()
break
}
if !isDigit(r) {
return 0, fmt.Errorf("non-integer value: %c", r)
}
number = append(number, r)
}
return strconv.Atoi(string(number))
}
func (sc *Scanner) read() rune {
ch, _, _ := sc.buf.ReadRune()
return ch
}
func (sc *Scanner) unread() { _ = sc.buf.UnreadRune() }
func isWhitespace(ch rune) bool { return ch == ' ' || ch == '\t' || ch == '\n' }
func isDigit(r rune) bool {
return r >= '0' && r <= '9'
}