equals and such

lexer/lexer.go

@@ -34,13 +34,25 @@ func (l *Lexer) NextToken() token.Token {
 
 	switch l.ch {
 	case '=':
-		tok = newToken(token.ASSIGN, l.ch)
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			tok = token.Token{Type: token.EQ, Literal: string(ch) + string(l.ch)}
+		} else {
+			tok = newToken(token.ASSIGN, l.ch)
+		}
 	case '+':
 		tok = newToken(token.PLUS, l.ch)
 	case '-':
 		tok = newToken(token.MINUS, l.ch)
 	case '!':
-		tok = newToken(token.BANG, l.ch)
+		if l.peekChar() == '=' {
+			ch := l.ch
+			l.readChar()
+			tok = token.Token{Type: token.NOT_EQ, Literal: string(ch) + string(l.ch)}
+		} else {
+			tok = newToken(token.BANG, l.ch)
+		}
 	case '/':
 		tok = newToken(token.SLASH, l.ch)
 	case '*':
@@ -114,3 +126,11 @@ func (l *Lexer) readNumber() string {
 	}
 	return l.input[position:l.position]
 }
+
+func (l *Lexer) peekChar() byte {
+	if l.readPosition >= len(l.input) {
+		return 0
+	} else {
+		return l.input[l.readPosition]
+	}
+}

lexer/lexer_test.go

@@ -22,7 +22,9 @@ if (5 < 10) {
 } else {
     return false;
 }
-// [...]
+
+10 == 10;
+10 != 9;
 `
 
 	tests := []struct {
@@ -77,6 +79,31 @@ if (5 < 10) {
 		{token.GT, ">"},
 		{token.INT, "5"},
 		{token.SEMICOLON, ";"},
+		{token.IF, "if"},
+		{token.LPAREN, "("},
+		{token.INT, "5"},
+		{token.LT, "<"},
+		{token.INT, "10"},
+		{token.RPAREN, ")"},
+		{token.LBRACE, "{"},
+		{token.RETURN, "return"},
+		{token.TRUE, "true"},
+		{token.SEMICOLON, ";"},
+		{token.RBRACE, "}"},
+		{token.ELSE, "else"},
+		{token.LBRACE, "{"},
+		{token.RETURN, "return"},
+		{token.FALSE, "false"},
+		{token.SEMICOLON, ";"},
+		{token.RBRACE, "}"},
+		{token.INT, "10"},
+		{token.EQ, "=="},
+		{token.INT, "10"},
+		{token.SEMICOLON, ";"},
+		{token.INT, "10"},
+		{token.NOT_EQ, "!="},
+		{token.INT, "9"},
+		{token.SEMICOLON, ";"},
 		{token.EOF, ""},
 	}
 

token/token.go

@@ -26,6 +26,9 @@ const (
 	LT = "<"
 	GT = ">"
 
+	EQ     = "=="
+	NOT_EQ = "!="
+
 	//DELIM
 	COMMA     = ""
 	SEMICOLON = ";"