Thank Daniel and Sam! Below is a little conclusion:
1. When it comes to "for*/list", "in-values" can be used to introduce bindings just like "let".
2. "filter-map" can be a great alternative when "for/list" is considered. On 08/17/2014 07:59 PM, Sam Tobin-Hochstadt wrote:
This is what 'in-value' is for. Sam On Aug 17, 2014 5:07 AM, "Mark Wallace" <lotab...@gmail.com <mailto:lotab...@gmail.com>> wrote: Consider the following pseudocode: (for/list ([i ...] #:when <very complecated expr E>) <reference to the above expr E>) Can I bind that expression E and reference in the body of "for/list"? If expression E takes lots of time to finish, we would not want to compute it again :). I understand that there are workarounds like first collect all items of expression E and then use 'filter' to get interested items. However it would be a waste of memory if the number of interested items is small. So, any ideas? -- Best Regards, Mark Wallace. ____________________ Racket Users list: http://lists.racket-lang.org/__users <http://lists.racket-lang.org/users>
-- Best Regards, Mark Wallace. ____________________ Racket Users list: http://lists.racket-lang.org/users
