On Thursday, March 27, 2014 5:13:21 AM UTC+5:30, Steven D'Aprano wrote: > On Thu, 27 Mar 2014 09:24:49 +1100, Chris Angelico wrote:
> > wrote: > >> Now actual python > >> def sumjensen(i_get, i_set,lower,upper,exp): > >> tot = 0 > >> i_set(lower) > >> while i_get() <= upper: > >> tot += exp_get() > >> i_set(i_get() + 1) > >> return tot > >> i=0 > >> a=[3,4,5] > >> i_get = lambda : i > >> def i_set(val): > >> global i > >> i = val > >> exp_get = lambda : a[i_get()] > >> call as sumjensen(i_get, i_set, lower, upper, exp_get) > >> [Note that because of lambda's restriction to being only an expression > >> I have to make it a def because of need for global] > > You prove here that Python has first-class expressions in the same way > > that 80x86 assembly language has garbage collection. Sure, you can > > implement it using the primitives you have, but that's not support. > +1 > Any language can work around the lack of a language feature by sufficient > layers of indirection, but that's not the same as having that language > feature. > Beyond a certain minimum feature set, all languages are Turing complete, > and so in one sense are of equivalent power. But they're not all of equal > expressiveness. Python is awesome, it is very expressive, but there are > certain things you can't write directly in Python, and have to resort to > circumlocutions instead. Of course. And there are different grades of circumlocution -- of 'coding-up' -- a missing feature. Terry said: > One passes an unquoted expression in code by quoting it with either > lambda, paired quote marks (Lisp used a single '), Steven responded: > Passing *strings* and *functions* is not the same as having compiler > support for delayed evaluation. At best its a second-class work-around. I was merely pointing out that 'passing strings' and 'passing functions' as 'coding-up' of some desirable but unavailable feature are very different levels of work-around. In fact there are actually 3 styles and levels of circumlocution 1. You dont have a certain language -- blub?? -- feature set. So... code it up and write its interpreter as eval_blub. 2. You dont have a feature-set but can see similarity in some obtuse host-language (in this case python). So you code up a mini-translator for your feature-set neatly written to obtuse hostly written and then eval (note python eval not blub eval) 3. You dont go outside the language framework and into any eval-ish mode at all. Good ol subroutine libraries to classes for abstraction to first-class functional abstraction -- all fall into this category -- https://mail.python.org/mailman/listinfo/python-list
