From: Duncan Mak <duncanmak@gmail.com>
To: Per Bothner <per@bothner.com>
Cc: kawa mailing list <kawa@sourceware.org>
Subject: Re: Extending functional call syntax for Sequences to include Maps
Date: Sat, 4 Jul 2020 00:07:44 -0400 [thread overview]
Message-ID: <CABgWrqpBnzZDULWpKx9OCw1-WfXz+saajHDNMMyCZoupXkcvDA@mail.gmail.com> (raw)
In-Reply-To: <b5d0a614-e40a-4728-6c9b-4989ee08d9a8@bothner.com>
I think with an optional keyword argument, this could look quite nice!
(aMap "key" default: "default value")
The keyword could be 'default', or even 'or'.
(aMap 'key or: "empty")
On Fri, Jul 3, 2020 at 6:05 PM Per Bothner <per@bothner.com> wrote:
> On 7/3/20 2:24 PM, Duncan Mak via Kawa wrote:
> > More concisely, you can use (Kawa-specific) function call syntax:
> >
> > (vec1 3) ⇒ 8
> >
> >
> > I was a little disappointed when I found out that this doesn't work for
> > Maps, which is also something Clojure allows [0]:
> >
> > ;; This is Clojure not Scheme
> >
> > ({:age 42 :name "Joe"} :name) ; ⇒ "Joe"
> > ({:age 42 :name "Joe"} :age) ; ⇒ 42
> > ({:age 42 :name "Joe"} :unknown) ; ⇒ nil
>
> I vaguely remember discussing this some years ago, and I think the main
> (conceptual) problem is how to handle arguments with no binding, i.e.
> the 3rd case above. By analogy with sequences, it should throw an
> exception - which may not be the most convenient
>
> I mentioned a couple of possible approaches, but I don't recall
> what they were. I think I was leaning towards a way to specify
> a default value - and throw an exception when no default was specified.
>
> I haven't been able to find that email, so far.
>
> A possibly solution:
>
> (htab key [default])
>
> If there is no entry for key in htab, then default is returned
> if specified; otherwise an exception is thrown.
>
> You should also be able to do:
>
> (set! (htab key) new-value)
> --
> --Per Bothner
> per@bothner.com http://per.bothner.com/
>
--
Duncan.
next prev parent reply other threads:[~2020-07-04 4:08 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-03 21:24 Duncan Mak
2020-07-03 22:05 ` Per Bothner
2020-07-04 4:07 ` Duncan Mak [this message]
2020-07-15 18:44 ` Jamison Hope
2020-07-16 5:24 ` Per Bothner
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