Rearrange control expression parsing

Parser.cs

@@ -163,6 +163,25 @@ class Parser
 		return ifExpr();
 	}
 
+	private Expr control()
+	{
+		switch (peek().type)
+		{
+			case TokenType.If:
+				advance();
+				Expr condition = expression();
+				consume(TokenType.Then, "Expect 'then' after condition.");
+				Expr thenCase = expression();
+				consume(TokenType.Else, "Expect 'else' after 'then' case.");
+				Expr elseCase = expression();
+				return new If { Condition = condition, Then = thenCase, Else = elseCase };
+			case TokenType.When:
+				throw new NotImplementedException();
+		}
+
+		return primary();
+	}
+
 	private Expr ifExpr()
 	{
 		if (match(TokenType.If))