or a macro
(defmacro defkargs [name destrt & body]
`(clojure.core/defn ~name
([] (~name {}))
([a# b# & {:as r#}]
(~name (clojure.core/assoc r# a# b#)))
([~destrt]
~@body)))
(defkargs kargs-test {:keys [some me]}
(when (and some me)
(+ some me)))
(and (= (kargs-test :some 1 :me 2)
(kargs-test {:some 1 :me 2})
3)
(= (kargs-test)
nil))
On Friday, March 13, 2015 at 1:46:08 PM UTC-4, Dylan Butman wrote:
>
> Late chime in...how about both?
>
> (defn kargs
> ([] (kargs {}))
> ([a b & {:as r}]
> (kargs (assoc r a b)))
> ([a] a))
>
> On Thursday, May 1, 2014 at 12:21:03 AM UTC-4, Jim Crossley wrote:
>>
>> Oh, right. (f m) instead of (apply f [m]). Duh.
>>
>>
>> On Wed, Apr 30, 2014 at 11:15 PM, Colin Fleming <[email protected]>
>> wrote:
>>
>>> I think it would because in that case you'd just pass your arg map
>>> straight through rather than having to reconstruct it. So if you weren't
>>> passed :y in g (in Mark's example), g wouldn't pass it on to f. By forcing
>>> the reconstruction of the map from explicit args, you're forced to use the
>>> value (incorrectly) destructured in g. Mark could work around it in his
>>> example by using (apply f (mapcat identity m)) in g, but it's far from
>>> intuitive.
>>>
>>>
>>> On 1 May 2014 15:04, Jim Crossley <[email protected]> wrote:
>>>
>>>> Unless I'm missing something subtle, all of your points would hold if
>>>> you removed the & in your argument vector to turn your kwargs into an
>>>> explicit map, wouldn't they? One advantage is you'd be able to (apply f
>>>> [m]), but I'm not sure the :or logic would be any less troublesome.
>>>>
>>>>
>>>> On Wed, Apr 30, 2014 at 8:06 PM, Mark Engelberg <[email protected]>
>>>> wrote:
>>>>
>>>>> Here's the thing I can't stand about keyword args:
>>>>>
>>>>> Let's start off with a simple function that looks for keys x and y,
>>>>> and if either is missing,
>>>>> replaces the value with 1 or 2 respectively.
>>>>>
>>>>> (defn f [& {:keys [x y] :or {x 1 y 2}}]
>>>>> [x y])
>>>>>
>>>>> => (f :x 10)
>>>>> [10 2]
>>>>>
>>>>> So far, so good.
>>>>>
>>>>> Now, let's do an extremely simple test of composability. Let's define
>>>>> a function g that destructures the keyword args, and if a certain keyword
>>>>> :call-f is set, then we're just going to turn around and call f, passing
>>>>> all the keyword args along to f.
>>>>>
>>>>> (defn g [& {call-f :call-f :as m}]
>>>>> (when call-f
>>>>> (apply f m)))
>>>>>
>>>>> => (g :call-f true :x 10)
>>>>> [1 2]
>>>>>
>>>>> What? Oh right, you can't apply the function f to the map m. This
>>>>> doesn't work. If we want to "apply" f, we somehow need to apply it to a
>>>>> sequence of alternating keys and values, not a map.
>>>>>
>>>>> Take 2:
>>>>>
>>>>> (defn g [& {:keys [call-f x y] :as m}]
>>>>> (when call-f
>>>>> (f :x x :y y)))
>>>>>
>>>>> OK, so this time we try to workaround things by explicitly calling out
>>>>> the names of all the keywords we want to capture and pass along. It's
>>>>> ugly, and doesn't seem to scale well to situations where you have an
>>>>> unknown but at first glance, it seems to work:
>>>>>
>>>>> => (g :call-f true :x 80 :y 20)
>>>>> [80 20]
>>>>>
>>>>> Or does it?
>>>>>
>>>>> => (g :call-f true :x 10)
>>>>> [10 nil]
>>>>>
>>>>> What is going on here? Why is the answer coming out that :y is nil,
>>>>> when function f explicitly uses :or to have :y default to 2?
>>>>>
>>>>> The answer is that :or doesn't do what you think it does. The word
>>>>> "or" implies that it substitutes the default value of :y any time the
>>>>> destructured :y is nil or false. But that's not how it really works. It
>>>>> doesn't destructure and then test against nil; instead the :or map only
>>>>> kicks in when :y is actually missing as a key of the map.
>>>>>
>>>>> This means that in g, when we actively destructured :y, it got set to
>>>>> a nil, and then that got passed along to f. f's :or map didn't kick in
>>>>> because :y was set to nil, not absent.
>>>>>
>>>>> This is awful. You can't pass through keyword arguments to other
>>>>> functions without explicitly destructuring them, and if you destructure
>>>>> them and pass them along explicitly, nil values aren't picked up as
>>>>> absent
>>>>> values, so the :or default maps don't work properly.
>>>>>
>>>>> To put it simply, keyword args are bad news for composability.
>>>>>
>>>>> It's a shame, and I'd love to see this improved (rather than just
>>>>> having the community give up on keyword arguments).
>>>>>
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>>>>
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>>>
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>>
>>
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