instructions.md

Work is progressing well at Instruments of Texas on the RPN Calculator. Your team now wants to be after to write a string version of the equation to an IO resource.

1. Open a file

Your team hasn't decided what type of device to write the equation to, so you suggest using a dynamic dispatch approach to be able to inject the resource into the function rather than hard-code it in. Implement the write/3 function to open an io_device handle using the resource and the filename.

You can assume resource will always be an atom that represents a module which has an open/1 function when returns a handler.

When the function succeeds, return an ok-tuple with the equation written

RPNCalculator.Output.write(resource, "file_to_be_written", "1 4 +")
# {:ok, "1 4 +"}

2. Attempt to write to the file

Now that you've opened the file, attempt to write to it using IO.write/2.

Extend the write/3 function to perform this action. The write action attempt may raise an error, rescue from the error returning an error-tuple:

RPNCalculator.Output.write(resource, "bad_file", "1 4 +")
# {:error, "Unable to write to resource"}

3. Close the file

It is a good practice to always try to release resources that you have opened, release the file opened by closing it, even if the function raises an error. Extend the write/3 function to call the resource's close function to close the io handler.

You can assume resource will always be an atom that represents a module which has a close/1 function which takes a handler.