UPDATE: the original links no longer work, but some of the PragPub content from a range of authors is being added to Medium, see https://medium.com/@pragpub.
See https://medium.com/search?q=callaghan+pragpub for a list of articles by me which have been uploaded there so far.
For convenience (mostly mine), here’s a list of the articles I wrote a few years ago.
Three of these articles have also been updated and published in book form! Please see Functional Programming: A PragPub Anthology. The book also includes interesting material about other functional languages and styles, and it’s a great introduction to current trends.
There’s another article about “Coercive Subtyping” which appeared in the August 2016 issue of PragPub. This issue is available for a modest fee (which covers the editing and production costs, not profit for me!) from http://theprosegarden.com/. Or you can email me to remind me to post a text copy of my article…