On 07/01/2012 09:27 AM, Eli Barzilay wrote:
There rare cases where it is useful to have a value that means that no
argument was passed to a function. In many of these cases there is a
plain value that is used as that mark, with the most idiomatic one
being #f, but sometimes others are used.
At Sun, 8 Jul 2012 08:40:41 -0400,
Eli Barzilay wrote:
Quick summary: I'll remove the #:before-first and #:after-last
feature. If anyone wants them, please tell me -- maybe it can be left
for the spliced case, or maybe they could always be spliced.
+2 to always splicing.
This gives us the
Quick summary: I'll remove the #:before-first and #:after-last
feature. If anyone wants them, please tell me -- maybe it can be left
for the spliced case, or maybe they could always be spliced.
On Monday, Matthew Flatt wrote:
I'm not enthusiastic about this proposal.
As you say at the
1. The need for a no-value initial value shows up only when we have a function
with two (or more) such parameters. Otherwise case-lambda does fine.
2. Eli's initial proposal triggered the same response in me as Robby's except
that our experience with 'undefined' immediately told me I want to
I really like this.
Vincent
At Sun, 1 Jul 2012 09:27:00 -0400,
Eli Barzilay wrote:
There rare cases where it is useful to have a value that means that no
argument was passed to a function. In many of these cases there is a
plain value that is used as that mark, with the most idiomatic
On 2012-07-01 09:27:00 -0400, Eli Barzilay wrote:
A more robust way to do that, which has become idiomatic in Racket is
to use (gensym). (And as a sidenote, in other implementations there
are various similar eq-based hacks.) IMO, this is an attempt to
improve on the #f case by guaranteeing a
I'm not enthusiastic about this proposal.
As you say at the start, it seems like a rare case. My main objection
is that it's too rare to merit a change to the main `lambda' form and
other parts of our infrastructure, such as documentation tools.
As a weaker objection, I don't agree with the
At Mon, 2 Jul 2012 12:14:02 -0400, Asumu Takikawa wrote:
The gensym thing is used in parts of the GUI code for initialization
arguments, e.g.:
(class* mred% (area%)
(init mk-wx get-wx-pan get-outer-wx-pan mismatches prnt
[min-width no-val]
[min-height no-val]
May be the discussion goes beyond my understanding, in which case sorry for
my noise. Where I need a value distinct from all other values (such as a
no-value), I prepare an empty struct type and export one single instance of
this struct together with its predicate (and nothing else)
Jos
There rare cases where it is useful to have a value that means that no
argument was passed to a function. In many of these cases there is a
plain value that is used as that mark, with the most idiomatic one
being #f, but sometimes others are used. IMO, while such uses of #f
are idiomatic,
If you're only going to use in keyword arguments (and optional
arguments), you could make it an error to touch the value, unless it
gets touched by a special predicate that checks for its existence.
That is, in
(define (f #:x [x]) ...)
(where I'm saying that leaving off the default value means
Just now, Robby Findler wrote:
If you're only going to use in keyword arguments (and optional
arguments), you could make it an error to touch the value, unless it
gets touched by a special predicate that checks for its existence.
That is, in
(define (f #:x [x]) ...)
(where I'm saying
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