137 lines
2.6 KiB
Go
137 lines
2.6 KiB
Go
package lexer
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import (
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"gitlab.com/Tyrel/monkey/token"
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)
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type Lexer struct {
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input string
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position int
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readPosition int
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ch byte
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}
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func New(input string) *Lexer {
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l := &Lexer{input: input}
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l.readChar()
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return l
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}
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func (l *Lexer) readChar() {
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if l.readPosition >= len(l.input) {
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l.ch = 0
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} else {
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l.ch = l.input[l.readPosition]
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}
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l.position = l.readPosition
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l.readPosition += 1
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}
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func (l *Lexer) NextToken() token.Token {
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var tok token.Token
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l.skipWhitespace()
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switch l.ch {
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case '=':
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if l.peekChar() == '=' {
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ch := l.ch
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l.readChar()
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tok = token.Token{Type: token.EQ, Literal: string(ch) + string(l.ch)}
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} else {
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tok = newToken(token.ASSIGN, l.ch)
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}
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case '+':
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tok = newToken(token.PLUS, l.ch)
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case '-':
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tok = newToken(token.MINUS, l.ch)
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case '!':
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if l.peekChar() == '=' {
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ch := l.ch
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l.readChar()
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tok = token.Token{Type: token.NOT_EQ, Literal: string(ch) + string(l.ch)}
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} else {
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tok = newToken(token.BANG, l.ch)
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}
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case '/':
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tok = newToken(token.SLASH, l.ch)
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case '*':
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tok = newToken(token.ASTERISK, l.ch)
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case '<':
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tok = newToken(token.LT, l.ch)
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case '>':
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tok = newToken(token.GT, l.ch)
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case '(':
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tok = newToken(token.LPAREN, l.ch)
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case ')':
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tok = newToken(token.RPAREN, l.ch)
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case '{':
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tok = newToken(token.LBRACE, l.ch)
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case '}':
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tok = newToken(token.RBRACE, l.ch)
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case ',':
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tok = newToken(token.COMMA, l.ch)
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case ';':
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tok = newToken(token.SEMICOLON, l.ch)
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case 0:
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tok.Literal = ""
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tok.Type = token.EOF
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default:
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if isLetter(l.ch) {
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tok.Literal = l.readIdentifier()
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tok.Type = token.LookupIdent(tok.Literal)
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return tok
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} else if isDigit(l.ch) {
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tok.Type = token.INT
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tok.Literal = l.readNumber()
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return tok
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} else {
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tok = newToken(token.ILLEGAL, l.ch)
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}
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}
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l.readChar()
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return tok
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}
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func newToken(tokenType token.TokenType, ch byte) token.Token {
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return token.Token{Type: tokenType, Literal: string(ch)}
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}
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func (l *Lexer) readIdentifier() string {
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position := l.position
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for isLetter(l.ch) {
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l.readChar()
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}
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return l.input[position:l.position]
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}
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func isLetter(ch byte) bool {
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return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
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}
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func isDigit(ch byte) bool {
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return '0' <= ch && ch <= '9'
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}
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func (l *Lexer) skipWhitespace() {
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for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
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l.readChar()
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}
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}
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func (l *Lexer) readNumber() string {
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position := l.position
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for isDigit(l.ch) {
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l.readChar()
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}
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return l.input[position:l.position]
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}
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func (l *Lexer) peekChar() byte {
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if l.readPosition >= len(l.input) {
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return 0
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} else {
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return l.input[l.readPosition]
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}
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}
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