diff --git a/lexer/lexer.go b/lexer/lexer.go
index 157a406..1342ac9 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -5,6 +5,8 @@ import "moodeng/token"
 func (l *Lexer) NextToken() token.Token {
 	var tok token.Token
 
+	l.skipWhitespace()
+
 	switch l.ch {
 	case '=':
 		tok = newToken(token.ASSIGN, l.ch)
@@ -28,6 +30,11 @@ func (l *Lexer) NextToken() token.Token {
 	default:
 		if isLetter(l.ch) {
 			tok.Literal = l.readIdentifier()
+			tok.Type = token.LookupIdent(tok.Literal)
+			return tok
+		} else if isDigit(l.ch) {
+			tok.Type = token.INT
+			tok.Literal = l.readNumber()
 			return tok
 		} else {
 			tok = newToken(token.ILLEGAL, l.ch)
@@ -76,3 +83,21 @@ func (l *Lexer) readIdentifier() string {
 func isLetter(ch byte) bool {
 	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_'
 }
+
+func (l *Lexer) skipWhitespace() {
+	for l.ch == ' ' || l.ch == '\t' || l.ch == '\r' || l.ch == '\n' {
+		l.readChar()
+	}
+}
+
+func (l *Lexer) readNumber() string {
+	position := l.position
+	for isDigit(l.ch) {
+		l.readChar()
+	}
+	return l.input[position:l.position]
+}
+
+func isDigit(ch byte) bool {
+	return '0' <= ch && ch <= '9'
+}
diff --git a/lexer/lexer_test.go b/lexer/lexer_test.go
index 88e02da..209ce1e 100644
--- a/lexer/lexer_test.go
+++ b/lexer/lexer_test.go
@@ -7,16 +7,14 @@ import (
 )
 
 func TestNextToken(t *testing.T) {
-	input := `
-	let five = 5;
-	let ten = 10;
+	input := `let five = 5;
+let ten = 10;
 
-	let add = fn(x, y) {
-		x + y;
-	};
+let add = fn(x, y) {
+x + y;
+};
 
-	let result = add(five, ten);
-	`
+let result = add(five, ten);`
 
 	tests := []struct {
 		expectedType    token.TokenType
diff --git a/token/token.go b/token/token.go
index 6f415bf..218eee2 100644
--- a/token/token.go
+++ b/token/token.go
@@ -7,6 +7,18 @@ type Token struct {
 	Literal string
 }
 
+var keywords = map[string]TokenType{
+	"fn":  FUNCTION,
+	"let": LET,
+}
+
+func LookupIdent(ident string) TokenType {
+	if tok, ok := keywords[ident]; ok {
+		return tok
+	}
+	return IDENT
+}
+
 const (
 	ILLEGAL = "ILLEGAL"
 	EOF     = "EOF"