[racket-dev] sequence syntax for (mlist #t #f …) ?

From: John Clements (clements at brinckerhoff.org)
Date: Thu Jun 21 12:00:13 EDT 2012

On Jun 21, 2012, at 1:34 AM, Robby Findler wrote:

> I usually in-naturals and zero? to do this.

Ah! That's nice. I can use that.

> I see that one example (that I didn't write is in base-render.rkt
>    (define/public (render-nested-flow i part ri starting-item?)
>      (for/list ([b (in-list (nested-flow-blocks i))]
>                 [pos (in-naturals)])
>        (render-block b part ri (and starting-item? (zero? pos)))))
> Robby
> On Thu, Jun 21, 2012 at 3:24 AM, Eli Barzilay <eli at barzilay.org> wrote:
>> An hour and a half ago, John Clements wrote:
>>> Reality check before I do something dumb and re-invent the wheel:
>>> I often want to write a for loop where the first element is treated
>>> specially. In such cases, it would be nice to have a sequence that
>>> had a #t and then an infinite number of #f's, so I could write
>>> (for ([s my-sequence] [first? <true-then-always-falses>]) …)
>> What are you using it for?  (Out of curiosity, I wonder if there's any
>> need for this that doesn't fall under what `add-between' does.)

Nothing unusual; I'm writing newlines in between rendered expressions in the stepper. I don't think an add-between would make for more readable code in this case, but it's a related use.


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