You will have to ask Rich. The two reasons I mentioned in my post were
my own guesses. I don't find either of them very persuasive myself. My
preference would be that patterns and literals should reflect each
other directly as much as possible. Features like :keys and :or have
no counterpart in the literal syntax and so impose no symmetry
constraints.
-Per
On Fri, Apr 16, 2010 at 9:25 PM, Asim Jalis <asimja...@gmail.com> wrote:
> On Fri, Apr 16, 2010 at 2:15 AM, Per Vognsen <per.vogn...@gmail.com> wrote:
>> What may confuse is that map destructuring swaps the positions of keys
>> and values as compared to map literals:
>>
>> user> (let [{x :body} {:body 42}]
>> x)
>> 42
>>
>> It does conform to the pattern that the bound variable precedes the
>> value to bind in forms like let. A benefit of this ordering is that
>> destructuring patterns like {:keys [a b c]} are unambiguous.
>
>
> Hi Per,
>
> Could you explain the rationale for this swapping? Intuitively it
> seems to me that (let [{ :body x } { :body 42 }] x) should bind x
> to 42 -- it seems intuitive because it is binding :body to :body
> and 42 to x.
>
> I realize that this doesn't work. I want to understand why. Why
> is (let [{ x :body } { :body 42 }] x) the correct way?
>
> Asim
>
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