On 7/11/10 9:08 PM, Michał Marczyk wrote:
On 12 July 2010 02:37, Jeffrey Schwab<j...@schwabcenter.com> wrote:
I did not know whether the sequence expressions (the right halves of the
binding-forms) were evaluated strictly, or re-evaluated on each pass (like
the body-expr). They are apparently evaluated a priori, when the
comprehension is defined:
Actually the example I posted previously demonstrates that this is not
the case. Here's another one:
user=> (def a (atom #{1 2}))
#'user/a
user=> (def f (for [i (range 2) j @a] [i j]))
#'user/f
user=> (swap! a disj 1 2)
#{}
user=> f
()
...whereas without the intervening swap!...
user=> f
([0 1] [0 2] [1 1] [1 2])
Only the outermost expression is evaluated up front.
Wow, that's non-intuitive. Thanks!
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