diff --git a/lexer/lexer.go b/lexer/lexer.go
index 0914b72..d1f55d5 100644
--- a/lexer/lexer.go
+++ b/lexer/lexer.go
@@ -41,6 +41,20 @@
 			continue
 		}
 
+		// Identifier: starts with letter, continues with letters/digits.
+		if isLetter(ch) {
+			start := i
+			for i < len(input) && (isLetter(input[i]) || isDigit(input[i])) {
+				i++
+			}
+			tokens = append(tokens, token.Token{
+				Type:    token.Ident,
+				Literal: input[start:i],
+				Pos:     start,
+			})
+			continue
+		}
+
 		// Single-character tokens.
 		var typ token.Type
 		switch ch {
@@ -56,6 +70,10 @@
 			typ = token.LParen
 		case ')':
 			typ = token.RParen
+		case ',':
+			typ = token.Comma
+		case '=':
+			typ = token.Equals
 		default:
 			return nil, fmt.Errorf("unexpected character %q at position %d", string(ch), i)
 		}
@@ -81,3 +99,7 @@
 func isDigit(ch byte) bool {
 	return ch >= '0' && ch <= '9'
 }
+
+func isLetter(ch byte) bool {
+	return (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_'
+}