Chris Alexander

On Engineering

Building F# to open the New York Times

19th February, 2017

Each day, the New York Times publishes its front page online. I find this a good place to get an overview of the news compared to their homepage which isn’t quite so clear in terms of overall headlines.

I thought I would write a bit of code to help launch the front pages, as navigating to the thumbnails or PDFs is a bit of a chore from the website.

NYT publishes six images per day; PDF and JPG formats of the New York, National (USA) and International papers. Here are some example links for today:

In line with my recent adventures, it’s time to start off with a model for this. It turns out it’s not that much work - we have two discriminated unions of the edition and format:

So now we need to build the links to the individual editions based on what you request with the model.

The links break down into three components: the bit up to “nytfrontpage”, the base path; the filename; then the file extension. We can write functions to provide these parts, given the input.

To begin with the base path:

Note how this implementation performs string formatting to put a date object into the correct format in the URI.

The next step is the file name, which depends on the edition, and then the date in the international edition:

For some reason the international edition also has the date in the filename, so that is applied here.

The final bit of the URI is the file extension, which is essentially a mapping:

The three components we need to build the URI are the edition, format and date; so we create a function which applies the three conversions we have above to build the full URI:

So we can now invoke the function in this way in order to get a URI:

We can take advantage of functional programming’s partial application to create some nice helper functions.

For example, the first here partially applies getFile to always work with the current day. The second example here creates a function with no arguments which gets today’s New York edition PDF.

We can also write a function to open a link in the default browser:

Finally, we can combine it all together to launch today’s New York PDF in the default browser: