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|
package compiler
import (
"bufio"
"fmt"
"io"
)
type tokenKind string
const (
tokenKindChar = tokenKind("char")
tokenKindAnyChar = tokenKind(".")
tokenKindRepeat = tokenKind("*")
tokenKindRepeatOneOrMore = tokenKind("+")
tokenKindOption = tokenKind("?")
tokenKindAlt = tokenKind("|")
tokenKindGroupOpen = tokenKind("(")
tokenKindGroupClose = tokenKind(")")
tokenKindBExpOpen = tokenKind("[")
tokenKindInverseBExpOpen = tokenKind("[^")
tokenKindBExpClose = tokenKind("]")
tokenKindCharRange = tokenKind("-")
tokenKindEOF = tokenKind("eof")
)
type token struct {
kind tokenKind
char rune
}
const nullChar = '\u0000'
func newToken(kind tokenKind, char rune) *token {
return &token{
kind: kind,
char: char,
}
}
type lexerMode string
const (
lexerModeDefault = lexerMode("default")
lexerModeBExp = lexerMode("bracket expression")
)
type rangeState string
// [a-z]
// ^^^^
// |||`-- ready
// ||`-- expect range terminator
// |`-- read range initiator
// `-- ready
const (
rangeStateReady = rangeState("ready")
rangeStateReadRangeInitiator = rangeState("read range initiator")
rangeStateExpectRangeTerminator = rangeState("expect range terminator")
)
type lexer struct {
src *bufio.Reader
peekChar2 rune
peekEOF2 bool
peekChar1 rune
peekEOF1 bool
lastChar rune
reachedEOF bool
prevChar1 rune
prevEOF1 bool
prevChar2 rune
pervEOF2 bool
mode lexerMode
rangeState rangeState
}
func newLexer(src io.Reader) *lexer {
return &lexer{
src: bufio.NewReader(src),
peekChar2: nullChar,
peekEOF2: false,
peekChar1: nullChar,
peekEOF1: false,
lastChar: nullChar,
reachedEOF: false,
prevChar1: nullChar,
prevEOF1: false,
prevChar2: nullChar,
pervEOF2: false,
mode: lexerModeDefault,
rangeState: rangeStateReady,
}
}
func (l *lexer) next() (*token, error) {
c, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
return newToken(tokenKindEOF, nullChar), nil
}
switch l.mode {
case lexerModeBExp:
tok, err := l.nextInBExp(c)
if err != nil {
return nil, err
}
switch tok.kind {
case tokenKindBExpClose:
l.mode = lexerModeDefault
case tokenKindCharRange:
l.rangeState = rangeStateExpectRangeTerminator
case tokenKindChar:
switch l.rangeState {
case rangeStateReady:
l.rangeState = rangeStateReadRangeInitiator
case rangeStateExpectRangeTerminator:
l.rangeState = rangeStateReady
}
}
return tok, nil
default:
tok, err := l.nextInDefault(c)
if err != nil {
return nil, err
}
switch tok.kind {
case tokenKindBExpOpen:
l.mode = lexerModeBExp
l.rangeState = rangeStateReady
case tokenKindInverseBExpOpen:
l.mode = lexerModeBExp
l.rangeState = rangeStateReady
}
return tok, nil
}
}
func (l *lexer) nextInDefault(c rune) (*token, error) {
switch c {
case '*':
return newToken(tokenKindRepeat, nullChar), nil
case '+':
return newToken(tokenKindRepeatOneOrMore, nullChar), nil
case '?':
return newToken(tokenKindOption, nullChar), nil
case '.':
return newToken(tokenKindAnyChar, nullChar), nil
case '|':
return newToken(tokenKindAlt, nullChar), nil
case '(':
return newToken(tokenKindGroupOpen, nullChar), nil
case ')':
return newToken(tokenKindGroupClose, nullChar), nil
case '[':
c1, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindBExpOpen, nullChar), nil
}
if c1 != '^' {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindBExpOpen, nullChar), nil
}
c2, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindInverseBExpOpen, nullChar), nil
}
if c2 != ']' {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindInverseBExpOpen, nullChar), nil
}
err = l.restore()
if err != nil {
return nil, err
}
err = l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindBExpOpen, nullChar), nil
case ']':
return newToken(tokenKindBExpClose, nullChar), nil
case '\\':
c, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
return nil, &SyntaxError{
message: "incompleted escape sequence; unexpected EOF follows \\ character",
}
}
switch {
case c == '\\' || c == '.' || c == '*' || c == '+' || c == '?' || c == '|' || c == '(' || c == ')' || c == '[' || c == ']':
return newToken(tokenKindChar, c), nil
default:
return nil, &SyntaxError{
message: fmt.Sprintf("invalid escape sequence '\\%s'", string(c)),
}
}
default:
return newToken(tokenKindChar, c), nil
}
}
func (l *lexer) nextInBExp(c rune) (*token, error) {
switch c {
case '-':
if l.rangeState != rangeStateReadRangeInitiator {
return newToken(tokenKindChar, c), nil
}
c1, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindCharRange, nullChar), nil
}
if c1 != ']' {
err := l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindCharRange, nullChar), nil
}
err = l.restore()
if err != nil {
return nil, err
}
return newToken(tokenKindChar, c), nil
case ']':
return newToken(tokenKindBExpClose, nullChar), nil
case '\\':
c, eof, err := l.read()
if err != nil {
return nil, err
}
if eof {
return nil, &SyntaxError{
message: "incompleted escape sequence; unexpected EOF follows \\ character",
}
}
switch {
case c == '\\' || c == '^' || c == '-' || c == ']':
return newToken(tokenKindChar, c), nil
default:
return nil, &SyntaxError{
message: fmt.Sprintf("invalid escape sequence '\\%s'", string(c)),
}
}
default:
return newToken(tokenKindChar, c), nil
}
}
func (l *lexer) read() (rune, bool, error) {
if l.reachedEOF {
return l.lastChar, l.reachedEOF, nil
}
if l.peekChar1 != nullChar || l.peekEOF1 {
l.prevChar2 = l.prevChar1
l.pervEOF2 = l.prevEOF1
l.prevChar1 = l.lastChar
l.prevEOF1 = l.reachedEOF
l.lastChar = l.peekChar1
l.reachedEOF = l.peekEOF1
l.peekChar1 = l.peekChar2
l.peekEOF1 = l.peekEOF2
l.peekChar2 = nullChar
l.peekEOF2 = false
return l.lastChar, l.reachedEOF, nil
}
c, _, err := l.src.ReadRune()
if err != nil {
if err == io.EOF {
l.prevChar2 = l.prevChar1
l.pervEOF2 = l.prevEOF1
l.prevChar1 = l.lastChar
l.prevEOF1 = l.reachedEOF
l.lastChar = nullChar
l.reachedEOF = true
return l.lastChar, l.reachedEOF, nil
}
return nullChar, false, err
}
l.prevChar2 = l.prevChar1
l.pervEOF2 = l.prevEOF1
l.prevChar1 = l.lastChar
l.prevEOF1 = l.reachedEOF
l.lastChar = c
l.reachedEOF = false
return l.lastChar, l.reachedEOF, nil
}
func (l *lexer) restore() error {
if l.lastChar == nullChar && !l.reachedEOF {
return fmt.Errorf("the lexer failed to call restore() because the last character is null")
}
l.peekChar2 = l.peekChar1
l.peekEOF2 = l.peekEOF1
l.peekChar1 = l.lastChar
l.peekEOF1 = l.reachedEOF
l.lastChar = l.prevChar1
l.reachedEOF = l.prevEOF1
l.prevChar1 = l.prevChar2
l.prevEOF1 = l.pervEOF2
l.prevChar2 = nullChar
l.pervEOF2 = false
return nil
}
|
