Dear all, at haskell-café & plt-scheme. 1. THANK YOU VERY MUCH for enlightening comments about the terminology, student psychology, etc. I will get back to it in a second, for the moment I ask you very politely: survey the adressee list if you "reply-all". For people subscribing both Haskell and Scheme forums means 4 copies of your message, if you send the messages simultaneously to the private address of the previous author...!. I thought that a cross posting might have some merits, and I see now the nuisance. My deep apologies. 2. People suggest that the word return has been badly chosen. I have no strong opinion, I begin to agree... we had unit, result, people propose liftM, compute, deliver, etc. I wonder why return stuck? Just because it exists elsewhere? I believe not, it has some appeal, as Joe Fasel acknowledges. C. Reinke writes:
One way to look at the problem is that some of your students have concrete experience with `return' in different contexts, and that Haskell tries to make different things look similar here. You say "we worked with monads for several weeks" but, you being yourself, this was probably at a fairly abstract and general level, right?
No, not exactly. Being myself, just the opposite. There is *NO* more abstraction in my course than in Wadler's "Essence...". * I begin with a silly functional evaluator of a tree representing an arithmetic expression. * We recognize together with the students that a program may fail, and we introduce Maybe. They see thus a simple monadic generali- sation and the first non-trivial instance of return. We try to implement (in a sketchy way) a tracing generalisation as well. * They have parallelly a course of Prolog, so we play con mucho gusto with a few "non-deterministic" algorithms, such as standard combinatoric exercices : the generation of permutations, of the powerset, etc. On average the students seem to understand the idea and the implementation, and *mind you*: while writing their exercises <<a vista>> they duly corrected themselves when they were tempted to write "z" instead of "return z". ([] =-> [[]]). * We worked for a reasonable period with monadic parsers. The comment above is valid. Semantically they accepted the difference between "z" and "return z". I couldn't foresee any surprises. * They had to write a serious program in Haskell, so I gave them an introduction to Haskell I/O. They couldn't escape from *practical* Monads (although some of my students "perverted" [with my approval] the idea of writing a *syntactic* converter to Scheme, realizing it not in Haskell but in Scheme...) I spoke of course about types, but not simultaneously. We took advantage of the type inference, and the *type* of return has not been discussed explicitly sufficiently early. This is - I believe - my main, fundamental pedagogical fault! Yes Joe, I think this has been my own <<pons asinorum>>. If my compilation course survives all this affair (not obvious) I will try to remember Jón Fairbarn's suggestion (repeated by Manuel Chakravarty), and to discuss thoroughly the status of "C" imperative concepts, in order to prevent misunderstandings. C. Reinke again:
Unless you're one of Asimov's technicians of eternity, it is a bit difficult to change the history of programming languages, and assuming that the students pay for the opportunity to learn, you can't really fire them either..
Hm. We are all Technicians able to change the past, but since we do not live outside the System, we do it usually in the Orwellian way: we change the INTERPRETATION of the past. Things which were good (structural top-down programming) become bad (inadapted to object approach). Strong typing? A straitjacket for some, a salvation for the other. Scheme'ists add OO layers in order to facilitate the code reusing, and this smuggles in some typing. Dynamic typing in static languages became a folkloric, never-ending issue... The history of languages is full of "second thoughts". Who will first write a paper with a Wadlerian style [[but taken from earlier literature]] title: "Monads considered harmful" "Return should NOT return its argument" etc.? And in France students don't pay for the opportunity to learn. Regards. Jerzy Karczmarczuk Caen, France