Add all the files from the interpreter repo

Signed-off-by: jmug <u.g.a.mariano@gmail.com>

pkg/lexer/lexer.go

@@ -0,0 +1,160 @@
+package lexer
+
+import "code.jmug.me/jmug/interpreter-in-go/pkg/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) NextToken() token.Token {
+	l.skipWhitespace()
+	var tok token.Token
+	switch l.ch {
+	case '=':
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok.Type = token.EQ
+			tok.Literal = literal
+		} else {
+			tok = newToken(token.ASSIGN, l.ch)
+		}
+	case '+':
+		tok = newToken(token.PLUS, l.ch)
+	case '-':
+		tok = newToken(token.MINUS, l.ch)
+	case '!':
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			literal := string(ch) + string(l.ch)
+			tok.Type = token.NOT_EQ
+			tok.Literal = literal
+		} else {
+			tok = newToken(token.BANG, l.ch)
+		}
+	case '*':
+		tok = newToken(token.ASTERISK, l.ch)
+	case '/':
+		tok = newToken(token.SLASH, l.ch)
+	case '<':
+		tok = newToken(token.LT, l.ch)
+	case '>':
+		tok = newToken(token.GT, l.ch)
+	case ',':
+		tok = newToken(token.COMMA, l.ch)
+	case ';':
+		tok = newToken(token.SEMICOLON, l.ch)
+	case ':':
+		tok = newToken(token.COLON, l.ch)
+	case '(':
+		tok = newToken(token.LPAREN, l.ch)
+	case ')':
+		tok = newToken(token.RPAREN, l.ch)
+	case '{':
+		tok = newToken(token.LBRACE, l.ch)
+	case '}':
+		tok = newToken(token.RBRACE, l.ch)
+	case '[':
+		tok = newToken(token.LBRACKET, l.ch)
+	case ']':
+		tok = newToken(token.RBRACKET, l.ch)
+	case '"':
+		tok.Type = token.STRING
+		tok.Literal = l.readString()
+	case 0:
+		tok.Literal = ""
+		tok.Type = token.EOF
+	default:
+		if isLetter(l.ch) {
+			tok.Literal = l.readIdentifier()
+			tok.Type = token.LookupIdent(tok.Literal)
+			// Don't let it fall through because readIdentifier calls readChar.
+			return tok
+		} else if isDigit(l.ch) {
+			tok.Literal = l.readNumber()
+			tok.Type = token.INT
+			// Don't let it fall through because readNumber calls readChar.
+			return tok
+		} else {
+			tok = newToken(token.ILLEGAL, l.ch)
+		}
+	}
+	l.readChar()
+	return tok
+}
+
+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) peekChar() byte {
+	if l.readPosition >= len(l.input) {
+		return 0
+	}
+	return l.input[l.readPosition]
+}
+
+func (l *Lexer) readIdentifier() string {
+	position := l.position
+	for isLetter(l.ch) {
+		l.readChar()
+	}
+	// Slicing until l.position instead of readPosition because the last read
+	// char was not a letter.
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) readNumber() string {
+	position := l.position
+	for isDigit(l.ch) {
+		l.readChar()
+	}
+	// Slicing until l.position instead of readPosition because the last read
+	// char was not a letter.
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) readString() string {
+	// Don't include the quotes in the literal.
+	position := l.position + 1
+	l.readChar()
+	for l.ch != '"' && l.ch != 0 {
+		l.readChar()
+	}
+	return l.input[position:l.position]
+}
+
+func (l *Lexer) skipWhitespace() {
+	for l.ch == ' ' || l.ch == '\t' || l.ch == '\n' || l.ch == '\r' {
+		l.readChar()
+	}
+}
+
+func newToken(tokenType token.TokenType, ch byte) token.Token {
+	return token.Token{Type: tokenType, Literal: string(ch)}
+}
+
+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'
+}