I suppose it could prevent certain optimizations in parameter passing, forcing space for arguments to be allocated on the heap.
Sent from my iPad On Jan 8, 2012, at 12:42 PM, Danny Yoo <d...@cs.wpi.edu> wrote: > On Sun, Jan 8, 2012 at 3:23 PM, Jordan Schatz <jor...@noionlabs.com> wrote: >> This code runs, but I'm guessing that its not the "right way" to do it. >> >> (define (js-date [i (current-date)]) >> (let ([original-format (date-display-format)] >> [return ((λ () >> (date-display-format 'rfc2822) >> (date->string i #t)))]) >> (date-display-format original-format) >> return)) >> >> 1) In "some other language" using a function as the default value for an >> argument is inefficient and frowned upon. Is that the case in racket? > > Hi Jordan, > > Can you give an example of such a language? I'm curious. > > I'm not sure where the inefficiency would come from, unless computing > the default value expression's value is costly. > > According to the documentation in: > > http://docs.racket-lang.org/reference/lambda.html#(form._((lib._racket/private/base..rkt)._lambda)) > > with regards to "default-expr": "... if no such argument is provided, > the default-expr is evaluated to produce a value associated with id." > > From the reference docs, it sounds like that, unlike a language like > Python, the default value is evaluated for every use of the function, > rather than just once when the function's defined. We can experiment > with this: ____________________ Racket Users list: http://lists.racket-lang.org/users
