Just finished writing the tests for reading and writing files. You can check the script below. With the exception of making the connection syntax consistent with the rest of it, I am going to consider this feature complete, the next things to is to work on deployment (basically, a tool that allows to run the script :-) ).
public OrderID as int
public CustomerID as string
public EmployeeID as int
ConnectionString: "Data Source=localhost;Initial Catalog=ETL_Test; Integrated Security=SSPI;"
source OrdersFromDatabase, Connection="Database":
Command: "SELECT OrderID, CustomerID, EmployeeID FROM Orders"
Parameters.File = Write(Customers).To("output.txt")
cust = Customers(
OrdersFromDatabase >> OrdersFile