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lexer.go
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lexer.go
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package sql
import (
"regexp"
"strings"
"unicode"
"unicode/utf8"
)
const (
eof rune = 0 // a special rune
)
// The lexer in this package is inspired by Rob Pike's 2011 talk on
// writing lexers manually https://talks.golang.org/2011/lex.slide#1.
// It makes a significant simplification of the idea and doesn't use
// goroutines and channels.
type lexer struct {
input string // the string being scanned
start int // start position of this item
pos int // current position in the input
width int // width of last rune read from input
}
func newLexer(input string) *lexer {
return &lexer{input: input}
}
func (l *lexer) Error(e string) {
log.Panicf("start=%d, pos=%d : %s near %.10q\n", l.start, l.pos, e, l.input[l.start:])
}
func (l *lexer) emit(lval *sqlSymType, typ int) int {
lval.val = l.input[l.start:l.pos]
l.start = l.pos
return typ
}
func (l *lexer) next() (r rune) {
if l.pos >= len(l.input) {
l.width = 0
return eof
}
r, l.width = utf8.DecodeRuneInString(l.input[l.pos:])
l.pos += l.width
return r
}
func (l *lexer) backup() {
l.pos -= l.width // when next() return eof, l.width==0.
}
func (l *lexer) peek() rune {
r := l.next()
l.backup()
return r
}
func (l *lexer) skipSpaces() {
for r := l.next(); unicode.IsSpace(r); r = l.next() {
}
l.backup()
l.start = l.pos
}
func (l *lexer) Lex(lval *sqlSymType) int {
l.skipSpaces()
r := l.peek()
switch {
case unicode.IsLetter(r):
return l.lexIdentOrKeyword(lval)
case unicode.IsDigit(r):
return l.lexNumber(lval)
case r == '"':
return l.lexString(lval)
case strings.IndexRune("+-*/%<>=()[]{},;", r) >= 0:
return l.lexOperator(lval)
case r == eof:
return 0 // indicate the end of lexing.
}
log.Panicf("Lex: Unknown problem %s", l.input[l.start:])
return -1 // indicate an error
}
func (l *lexer) lexIdentOrKeyword(lval *sqlSymType) int {
// lexToken ensures that the first rune is a letter.
r := l.next()
for {
for unicode.IsLetter(r) || unicode.IsNumber(r) || r == '_' {
r = l.next()
}
if r != '.' { // The dot cannot be the last rune.
break
} else {
r = l.next()
}
}
l.backup()
return l.emitIdentOrKeyword(lval)
}
func (l *lexer) emitIdentOrKeyword(lval *sqlSymType) int {
keywds := map[string]int{
"SELECT": SELECT,
"FROM": FROM,
"WHERE": WHERE,
"LIMIT": LIMIT,
"TRAIN": TRAIN,
"PREDICT": PREDICT,
"USING": USING,
"WITH": WITH,
"COLUMN": COLUMN,
"LABEL": LABEL,
"INTO": INTO,
"AND": AND,
"OR": OR,
"NOT": NOT,
}
if typ, ok := keywds[strings.ToUpper(l.input[l.start:l.pos])]; ok {
return l.emit(lval, typ)
}
return l.emit(lval, IDENT)
}
var (
// Stolen https://www.regular-expressions.info/floatingpoint.html.
reNumber = regexp.MustCompile("[-+]?[0-9]*.?[0-9]+([eE][-+]?[0-9]+)?")
)
func (l *lexer) lexNumber(lval *sqlSymType) int {
m := reNumber.FindStringIndex(l.input[l.pos:])
if m == nil || m[0] != 0 {
log.Panicf("Expecting a number, but see %.10q", l.input[l.pos:])
}
l.pos += m[1]
return l.emit(lval, NUMBER)
}
func (l *lexer) lexOperator(lval *sqlSymType) int {
r := l.next()
if r == '*' && l.peek() == '*' {
l.next()
return l.emit(lval, POWER)
} else if r == '<' && l.peek() == '=' {
l.next()
return l.emit(lval, LE)
} else if r == '>' && l.peek() == '=' {
l.next()
return l.emit(lval, GE)
}
return l.emit(lval, int(r))
}
func (l *lexer) lexString(lval *sqlSymType) int {
l.next() // the left quote
for r := l.next(); r != '"'; r = l.next() {
if r == '\\' {
l.next()
}
}
return l.emit(lval, STRING)
}