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scanner.go
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scanner.go
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package scanner
import (
"bufio"
"io"
"unicode"
)
var eof = rune(0)
// Scanner represents a lexical scanner.
type Scanner struct {
r *bufio.Reader
lastReadBuffer []rune
lastScanRaw []rune
// pos is a current source position.
pos *Position
// The Mode field controls which tokens are recognized.
Mode Mode
}
// Option is an option for scanner.NewScanner.
type Option func(*Scanner)
// WithFilename is an option to set filename to the pos.
func WithFilename(filename string) Option {
return func(l *Scanner) {
l.pos.Filename = filename
}
}
// NewScanner returns a new instance of Scanner.
func NewScanner(r io.Reader, opts ...Option) *Scanner {
s := &Scanner{
r: bufio.NewReader(r),
pos: NewPosition(),
}
for _, opt := range opts {
opt(s)
}
return s
}
func (s *Scanner) read() (r rune) {
defer func() {
if r == eof {
return
}
s.lastScanRaw = append(s.lastScanRaw, r)
s.pos.Advance(r)
}()
if 0 < len(s.lastReadBuffer) {
var ch rune
ch, s.lastReadBuffer = s.lastReadBuffer[len(s.lastReadBuffer)-1], s.lastReadBuffer[:len(s.lastReadBuffer)-1]
return ch
}
ch, _, err := s.r.ReadRune()
if err != nil {
return eof
}
return ch
}
func (s *Scanner) unread(ch rune) {
s.lastReadBuffer = append(s.lastReadBuffer, ch)
s.pos.Revert(ch)
}
func (s *Scanner) peek() rune {
ch := s.read()
if ch != eof {
s.lastScanRaw = s.lastScanRaw[0 : len(s.lastScanRaw)-1]
s.unread(ch)
}
return ch
}
// UnScan put the last scanned text back to the read buffer.
func (s *Scanner) UnScan() {
var reversedRunes []rune
for _, ch := range s.lastScanRaw {
reversedRunes = append([]rune{ch}, reversedRunes...)
}
for _, ch := range reversedRunes {
s.unread(ch)
}
}
// Scan returns the next token and text value.
func (s *Scanner) Scan() (Token, string, Position, error) {
s.lastScanRaw = s.lastScanRaw[:0]
return s.scan()
}
// LastScanRaw returns the deep-copied lastScanRaw.
func (s *Scanner) LastScanRaw() []rune {
r := make([]rune, len(s.lastScanRaw))
copy(r, s.lastScanRaw)
return r
}
// SetLastScanRaw sets lastScanRaw to the given raw.
func (s *Scanner) SetLastScanRaw(raw []rune) {
s.lastScanRaw = raw
}
func (s *Scanner) scan() (Token, string, Position, error) {
ch := s.peek()
startPos := *s.pos
switch {
case unicode.IsSpace(ch):
s.read()
return s.scan()
case s.isEOF():
return TEOF, "", startPos, nil
case isLetter(ch), ch == '_':
ident := s.scanIdent()
if s.Mode&ScanBoolLit != 0 && isBoolLit(ident) {
return TBOOLLIT, ident, startPos, nil
}
if s.Mode&ScanNumberLit != 0 && isFloatLitKeyword(ident) {
return TFLOATLIT, ident, startPos, nil
}
if s.Mode&ScanKeyword != 0 && asKeywordToken(ident) != TILLEGAL {
return asKeywordToken(ident), ident, startPos, nil
}
return TIDENT, ident, startPos, nil
case ch == '/':
lit, err := s.scanComment()
if err != nil {
return TILLEGAL, "", startPos, err
}
if s.Mode&ScanComment != 0 {
return TCOMMENT, lit, startPos, nil
}
return s.scan()
case isQuote(ch) && s.Mode&ScanStrLit != 0:
lit, err := s.scanStrLit()
if err != nil {
return TILLEGAL, "", startPos, err
}
return TSTRLIT, lit, startPos, nil
case (isDecimalDigit(ch) || ch == '.') && s.Mode&ScanNumberLit != 0:
tok, lit, err := s.scanNumberLit()
if err != nil {
return TILLEGAL, "", startPos, err
}
return tok, lit, startPos, nil
default:
return asMiscToken(ch), string(s.read()), startPos, nil
}
}