Scanner working for single character tokens.

golox/internal/runner/scanner.go

@@ -0,0 +1,80 @@
+package runner
+
+type Scanner struct {
+	source string
+
+	// State.
+	tokens  []Token
+	start   int
+	current int
+	line    int
+}
+
+func NewScanner(source string) *Scanner {
+	return &Scanner{
+		source: source,
+		tokens: []Token{},
+
+		start:   0,
+		current: 0,
+		line:    1,
+	}
+}
+
+func (s *Scanner) ScanTokens() []Token {
+	for !s.isAtEnd() {
+		s.start = s.current
+		s.scanToken()
+	}
+
+	s.tokens = append(s.tokens, NewToken(EOF, "", nil, s.line))
+	return s.tokens
+}
+
+func (s *Scanner) scanToken() {
+	c := s.advance()
+	switch c {
+	case '(':
+		s.addToken(LPAREN)
+	case ')':
+		s.addToken(RPAREN)
+	case '{':
+		s.addToken(LBRACE)
+	case '}':
+		s.addToken(RBRACE)
+	case ',':
+		s.addToken(COMMA)
+	case '.':
+		s.addToken(DOT)
+	case '-':
+		s.addToken(MINUS)
+	case '+':
+		s.addToken(PLUS)
+	case ';':
+		s.addToken(SEMI)
+	case '*':
+		s.addToken(STAR)
+	}
+}
+
+func (s *Scanner) advance() byte {
+	idx := s.current
+	s.current += 1
+	return s.source[idx]
+}
+
+func (s *Scanner) addToken(typ TokenType) {
+	s.addTokenWithLiteral(typ, nil)
+}
+
+func (s *Scanner) addTokenWithLiteral(typ TokenType, literal interface{}) {
+	lexme := s.source[s.start:s.current]
+	s.tokens = append(
+		s.tokens,
+		NewToken(typ, lexme, literal, s.line),
+	)
+}
+
+func (s *Scanner) isAtEnd() bool {
+	return s.current >= len(s.source)
+}