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