Initial commit of lexer

lox/scanner.go

@@ -0,0 +1,140 @@
+package lox
+
+type Lexer struct {
+	start   int
+	current int
+	line    int
+	column  int
+	source  []rune
+	tokens  []Token
+}
+
+func (lexer Lexer) lex() {
+
+	for !lexer.eof() {
+		lexer.start = lexer.current
+		c := lexer.advance()
+
+		switch c {
+		case '(':
+			lexer.addToken(LeftParen)
+		case ')':
+			lexer.addToken(RightParen)
+		case '{':
+			lexer.addToken(LeftBrace)
+		case '}':
+			lexer.addToken(RightBrace)
+		case ',':
+			lexer.addToken(Comma)
+		case '.':
+			lexer.addToken(Dot)
+		case '-':
+			lexer.addToken(Minus)
+		case '+':
+			lexer.addToken(Plus)
+		case ';':
+			lexer.addToken(Semicolon)
+		case '*':
+			lexer.addToken(Star)
+		case '!':
+			if lexer.match('=') {
+				lexer.addToken(BangEqual)
+			} else {
+				lexer.addToken(Bang)
+			}
+		case '=':
+			if lexer.match('=') {
+				lexer.addToken(EqualEqual)
+			} else {
+				lexer.addToken(Equal)
+			}
+		case '<':
+			if lexer.match('=') {
+				lexer.addToken(LessEqual)
+			} else {
+				lexer.addToken(Less)
+			}
+		case '>':
+			if lexer.match('=') {
+				lexer.addToken(GreaterEqual)
+			} else {
+				lexer.addToken(Greater)
+			}
+		case '/':
+			if lexer.match('/') {
+				for lexer.peek() != '\n' && !lexer.eof() {
+					lexer.advance()
+				}
+			} else {
+				lexer.addToken(Slash)
+			}
+		case ' ', '\r', '\t': // Ignore whitespace
+			continue
+		case '\n':
+			lexer.line++
+			lexer.column = 0
+		case '"':
+			for lexer.peek() != '"' && !lexer.eof() {
+				if lexer.peek() == '\n' {
+					lexer.line++
+					lexer.column--
+				}
+				lexer.advance()
+			}
+
+			// if lexer.eof() {
+			// 	// Add error (unterminated string)
+			// }
+
+			// Consume the terminating "
+			lexer.advance()
+
+			//value := lexer.source[lexer.start+1 : lexer.current-1]
+			//lexer.addToken(String, value)
+		}
+	}
+	lexer.addToken(Eof)
+}
+
+func (s *Lexer) addToken(tt TokenType) {
+	s.tokens = append(s.tokens, *makeToken(tt, "", nil, s.line, s.column))
+}
+
+// eof returns true if the read pointer has reached the end of the source file
+func (s Lexer) eof() bool {
+	return s.current >= len(s.source)
+}
+
+// peek looks one rune ahead without advancing the cursor
+func (s Lexer) peek() rune {
+	if s.eof() {
+		return '\u0004' // emit end of file character
+	}
+	return s.source[s.current]
+}
+
+// advance increments the read pointer and returns the rune at that position
+func (s *Lexer) advance() rune {
+	r := s.source[s.current]
+	s.current++
+	s.column++
+	return r
+}
+
+// match tried to match a single rune and advances the read pointer if it does.
+func (s *Lexer) match(expected rune) bool {
+	if s.eof() {
+		return false
+	}
+	if s.source[s.current] != expected {
+		return false
+	}
+
+	s.current++
+	s.column++
+	return true
+}
+
+func newLexer(source string) *Lexer {
+	return &Lexer{line: 1, column: 0, source: []rune(source)}
+}