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lexer.go
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lexer.go
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package lexer
import (
"github.com/goby-lang/goby/compiler/token"
"github.com/looplab/fsm"
)
// Lexer is used for tokenizing programs
type Lexer struct {
input []rune
position int
readPosition int
ch rune
line int
FSM *fsm.FSM
}
// New initializes a new lexer with input string
func New(input string) *Lexer {
l := &Lexer{input: []rune(input)}
l.readChar()
l.FSM = fsm.NewFSM(
"initial",
/*
Initial state is default state
Nosymbol state helps us identify tok ':' is for symbol or hash value
Method state helps us identify 'class' literal is a keyword or an identifier
Reference: https://github.com/looplab/fsm
*/
fsm.Events{
{Name: "nosymbol", Src: []string{"initial"}, Dst: "nosymbol"},
{Name: "method", Src: []string{"initial"}, Dst: "method"},
{Name: "initial", Src: []string{"method", "initial", "nosymbol"}, Dst: "initial"},
},
fsm.Callbacks{},
)
return l
}
// NextToken makes lexer tokenize next character(s)
func (l *Lexer) NextToken() token.Token {
var tok token.Token
l.resetNosymbol()
l.skipWhitespace()
switch l.ch {
case '"', '\'':
tok.Literal = l.readString(l.ch)
tok.Type = token.String
tok.Line = l.line
return tok
case '=':
if l.peekChar() == '=' {
currentByte := l.ch
l.readChar()
tok = token.Token{Type: token.Eq, Literal: string(currentByte) + string(l.ch), Line: l.line}
} else if l.peekChar() == '~' {
currentByte := l.ch
l.readChar()
tok = token.Token{Type: token.Match, Literal: string(currentByte) + string(l.ch), Line: l.line}
} else {
tok = newToken(token.Assign, l.ch, l.line)
}
case '-':
if l.peekChar() == '=' {
tok.Literal = "-="
tok.Line = l.line
tok.Type = token.MinusEq
l.readChar()
l.readChar()
return tok
}
tok = newToken(token.Minus, l.ch, l.line)
case '!':
if l.peekChar() == '=' {
currentByte := l.ch
l.readChar()
tok = token.Token{Type: token.NotEq, Literal: string(currentByte) + string(l.ch), Line: l.line}
} else {
tok = newToken(token.Bang, l.ch, l.line)
}
case '/':
tok = newToken(token.Slash, l.ch, l.line)
case '*':
if l.peekChar() == '*' {
l.readChar()
tok = token.Token{Type: token.Pow, Literal: "**", Line: l.line}
} else {
tok = newToken(token.Asterisk, l.ch, l.line)
}
case '<':
if l.peekChar() == '=' {
l.readChar()
if l.peekChar() == '>' {
l.readChar()
tok = token.Token{Type: token.COMP, Literal: "<=>", Line: l.line}
} else {
tok = token.Token{Type: token.LTE, Literal: "<=", Line: l.line}
}
} else {
tok = newToken(token.LT, l.ch, l.line)
}
case '>':
if l.peekChar() == '=' {
l.readChar()
tok = token.Token{Type: token.GTE, Literal: ">=", Line: l.line}
} else {
tok = newToken(token.GT, l.ch, l.line)
}
case ';':
tok = newToken(token.Semicolon, l.ch, l.line)
case '(':
tok = newToken(token.LParen, l.ch, l.line)
case ')':
tok = newToken(token.RParen, l.ch, l.line)
case ',':
tok = newToken(token.Comma, l.ch, l.line)
case '+':
if l.peekChar() == '=' {
tok.Literal = "+="
tok.Line = l.line
tok.Type = token.PlusEq
l.readChar()
l.readChar()
return tok
}
tok = newToken(token.Plus, l.ch, l.line)
case '{':
tok = newToken(token.LBrace, l.ch, l.line)
case '}':
tok = newToken(token.RBrace, l.ch, l.line)
case '[':
tok = newToken(token.LBracket, l.ch, l.line)
case ']':
tok = newToken(token.RBracket, l.ch, l.line)
case '.':
if l.peekChar() == '.' {
tok = token.Token{Type: token.Range, Literal: "..", Line: l.line}
l.readChar()
l.readChar()
return tok
}
tok = newToken(token.Dot, l.ch, l.line)
l.FSM.Event("method")
case ':':
if l.FSM.Is("nosymbol") {
//e.g. {test: abc} || {test: :abc} || {test: 50}
tok = newToken(token.Colon, l.ch, l.line)
} else {
if l.peekChar() == ':' {
l.readChar()
tok = token.Token{Type: token.ResolutionOperator, Literal: "::", Line: l.line}
} else if isLetter(l.peekChar()) {
tok.Literal = string(l.readSymbol())
tok.Type = token.String
tok.Line = l.line
return tok
} else {
tok = newToken(token.Colon, l.ch, l.line)
}
}
case '|':
if l.peekChar() == '|' {
l.readChar()
if l.peekChar() == '=' {
l.readChar()
tok = token.Token{Type: token.OrEq, Literal: "||=", Line: l.line}
} else {
tok = token.Token{Type: token.Or, Literal: "||", Line: l.line}
}
} else {
tok = newToken(token.Bar, l.ch, l.line)
}
case '&':
if l.peekChar() == '&' {
l.readChar()
tok = token.Token{Type: token.And, Literal: "&&", Line: l.line}
}
case '%':
tok = newToken(token.Modulo, l.ch, l.line)
case '#':
tok.Literal = string(l.absorbComment())
tok.Type = token.Comment
tok.Line = l.line
return tok
case 0:
tok.Literal = ""
tok.Type = token.EOF
tok.Line = l.line
default:
if isLetter(l.ch) {
if 'A' <= l.ch && l.ch <= 'Z' {
tok.Literal = string(l.readConstant())
tok.Type = token.Constant
tok.Line = l.line
l.FSM.Event("initial")
} else {
tok.Literal = string(l.readIdentifier())
if l.FSM.Is("method") {
if tok.Literal == "self" {
tok.Type = token.LookupIdent(tok.Literal)
} else {
tok.Type = token.Ident
}
l.FSM.Event("initial")
} else if l.FSM.Is("initial") {
tok.Type = token.LookupIdent(tok.Literal)
if tok.Literal == "def" {
l.FSM.Event("method")
} else {
l.FSM.Event("initial")
}
}
tok.Line = l.line
}
if tok.Type == token.Ident {
l.FSM.Event("nosymbol")
}
return tok
} else if isInstanceVariable(l.ch) {
if isLetter(l.peekChar()) {
tok.Literal = string(l.readInstanceVariable())
tok.Type = token.InstanceVariable
tok.Line = l.line
return tok
}
return newToken(token.Illegal, l.ch, l.line)
} else if isDigit(l.ch) {
tok.Literal = string(l.readNumber())
tok.Type = token.Int
tok.Line = l.line
return tok
}
tok = newToken(token.Illegal, l.ch, l.line)
}
l.readChar()
return tok
}
func (l *Lexer) skipWhitespace() {
for l.ch == ' ' || l.ch == '\t' || l.ch == '\r' || l.ch == '\n' {
if l.ch == '\n' {
l.line++
}
l.readChar()
}
}
func (l *Lexer) resetNosymbol() {
if !l.FSM.Is("method") && l.ch != ':' {
l.FSM.Event("initial")
}
}
func (l *Lexer) readNumber() []rune {
position := l.position
for isDigit(l.ch) {
l.readChar()
}
return l.input[position:l.position]
}
func (l *Lexer) readIdentifier() []rune {
position := l.position
for isLetter(l.ch) || isDigit(l.ch) {
l.readChar()
}
if l.ch == '?' {
l.readChar()
}
return l.input[position:l.position]
}
func (l *Lexer) readConstant() []rune {
position := l.position
for isLetter(l.ch) || isDigit(l.ch) {
l.readChar()
}
return l.input[position:l.position]
}
func (l *Lexer) readInstanceVariable() []rune {
position := l.position
for isLetter(l.ch) || isInstanceVariable(l.ch) || isDigit(l.ch) {
l.readChar()
}
return l.input[position:l.position]
}
func (l *Lexer) readString(ch rune) string {
l.readChar()
// Empty strings case such as "" or ''
if l.ch == ch {
l.readChar()
return ""
}
result := ""
for {
if isEscapedChar(l.ch) {
result += escapedCharResult(ch, l.peekChar())
l.readChar()
} else {
result += string(l.ch)
}
l.readChar()
if l.ch == ch || l.peekChar() == 0 {
break
}
}
// fmt.Println(l.ch) <- Currently at string's last character
l.readChar() // move to string's latter quote
return result
}
func (l *Lexer) readSymbol() []rune {
l.readChar()
position := l.position // currently at string's first letter
for isLetter(l.peekChar()) || isDigit(l.peekChar()) {
l.readChar()
}
l.readChar() // currently at string's last letter
result := l.input[position:l.position] // get full string
return result
}
func (l *Lexer) absorbComment() []rune {
p := l.position
for l.ch != '\n' && l.ch != 0 {
l.readChar()
}
result := l.input[p:l.position]
return result
}
func (l *Lexer) readChar() {
if l.readPosition >= len(l.input) {
// ascii code's null
l.ch = 0
} else {
l.ch = l.input[l.readPosition]
}
l.position = l.readPosition
l.readPosition++
}
func (l *Lexer) peekChar() rune {
if l.readPosition >= len(l.input) {
return 0
}
return l.input[l.readPosition]
// Peek shouldn't increment positions.
}
func isDigit(ch rune) bool {
return '0' <= ch && ch <= '9'
}
func isLetter(ch rune) bool {
return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
}
func isInstanceVariable(ch rune) bool {
return ch == '@'
}
func isEscapedChar(ch rune) bool {
return ch == '\\'
}
func escapedCharResult(quotedChar rune, peeked rune) string {
if quotedChar == '"' {
switch peeked {
case 'n':
return "\n"
case 't':
return "\t"
case 'v':
return "\v"
case 'f':
return "\f"
case 'r':
return "\r"
case '\\':
return "\\"
case '"':
return "\""
case '\'':
return "'"
default:
return "\\" + string(peeked)
}
}
switch peeked {
case '"':
return "\\\""
case '\'':
return "'"
default:
return "\\" + string(peeked)
}
}
func newToken(tokenType token.Type, ch rune, line int) token.Token {
return token.Token{Type: tokenType, Literal: string(ch), Line: line}
}