More illustratively, I'd say he's more saying "go to France, then learn French as you go" versus the common programmer course of "learn French then never go there".
Learning Haskell, Erlang, Lisp, etc, can be interesting on its own, but if you instead try to achieve something or learn about a subject area where Haskell, Erlang, or Lisp are strong, it's a far better way of learning. Go to France and then learn French.
Are you sure you aren't inserting that message because it seems more reasonable?
That really doesn't seem like the message that's being stated. It is a little hard to pick out the relevant parts, but it seems like he's going to stick to what languages he knows and instead focus on solving problem domains.
Learning new languages as you explore new problem domains doesn't seem like the message in the post, at all.
You might be right, but he talks about using Seaside, which is based on Smalltalk. I've been following his blog for quite a while and haven't seen strong reference to learning Smalltalk, yet if you wanted to use Seaside's strengths to solve a certain problem, you would end up learning some Smalltalk en-route.
This is what I've been doing. I've been taking one computer science course per semester, and picking a language to learn to do the problems in. Well, actually, more like 4 semesters and 3 languages (Common Lisp for 2 semesters, Python and Clojure 1 each). This is in addition to doing Java as my day job, and trying to learn it better, too.
This has occasionally led to more excitement than I wanted, like trying to push Python to do a processing intensive task and then switching to Java at the last minute so it would finish by the deadline. But for the most part it has worked well and by picking more productive languages to learn has even made some tasks easier than they would have been with my day job language.
However, my goal for the new year is to start a blog and write more. One of the first topics I want to write about is the programming languages I've used and what I've learned from them.
Learning Haskell, Erlang, Lisp, etc, can be interesting on its own, but if you instead try to achieve something or learn about a subject area where Haskell, Erlang, or Lisp are strong, it's a far better way of learning. Go to France and then learn French.