While this book is an interesting and fairly comprehensive book on functional programming and music theory, I have the impression that the idea of algorithmic composition as expressed in this book is out of fashion now. Algorithmic composition was big in contemporary, "serious" music in the last part of the 20th century, but my contemporary composer friends seem to have left their Markov chains and Lisp algorithms and are now more into interactive stuff, with Processing and Arduino being a couple of the technologies du jour. It's not a clear-cut distinction, you can of course use Haskell and FP for interactive music creation and there will be various degrees of algorithmic composing in an interactive, computer based performance. But the possibilities of pure, computer generated music have largely been explored, decomposed down to sample-level granularity and recomposed using all thinkable sound generating algorithms. The cultural impact has been somewhere between weak and zero. People still prefer tonal music composed by humans.
I believe algorithmic composition has suffered the same fate as symbolic natural language processing. They are both interesting from an academic point of view, but have failed to produce the wanted end results. Computers have not given us new musical dimensions that anyone outside an academic, postmodernist following care to listen to. The hope (or threat, depending of how you view it) may lie in statistical approaches. Thorough statistical analyses of existing compositions and recomposition based on that, parallelling what Google translate does with natural language processing. As far as I know, there are companies and researchers working on that, so don't throw away those Markov chains yet.
Social constructivism again. Including, as usual: 1) cherry-picked statistics, 2) made-up anecdotal explanations without any scientific base, 3) a couple of dogmas about how it can and should be, and 4) a made-up solution wihout any scientific base.