Here's how I did it, which is similar to what atkaaz and Jim were
suggesting:
(defn whenever [x applies-to? f] (if (applies-to? x) (f x) x))
(whenever obj :attr #(assoc % :attr something))
(whenever obj some-test some-transformation)
On 25 May 2013 15:19, atkaaz <atk...@gmail.com> wrote:
>
>
>
> On Sat, May 25, 2013 at 3:16 PM, Steven Degutis <sbdegu...@gmail.com>wrote:
>
>>
>> Also I just remembered, sometimes to solve the second one, I would do ((if
>> condition transformer identity) obj) but that feels ugly.
>>
> but the condition has to contain obj, so obj is referred twice ? otherwise
> i kinda like it
>
>>
>>
>> On Sat, May 25, 2013 at 7:13 AM, Cedric Greevey <cgree...@gmail.com>wrote:
>>
>>> Seems to me that (merge {:attr something} obj) answers the OP's
>>> question, mentions obj only once, and is short and pithy. OTOH it computes
>>> the "something" every time, whether it's needed or not, so in cases where
>>> "something" is expensive to compute (or has side effects that should only
>>> happen if it winds up in the output!) then another method needs to be used.
>>>
>>>
>>> On Sat, May 25, 2013 at 8:08 AM, atkaaz <atk...@gmail.com> wrote:
>>>
>>>> like:
>>>> => (definline pred-transform [obj pred tf]
>>>> `(let [o# ~obj]
>>>> (if (~pred o#) o#
>>>> (~tf o#))))
>>>> #'cgws.notcore/pred-transform
>>>>
>>>> => (pred-transform (println 1) nil? #(println % "."))
>>>> 1
>>>> nil
>>>> => (pred-transform (println 1) #(not (nil? %)) #(println % "."))
>>>> 1
>>>> nil .
>>>> nil
>>>>
>>>>
>>>> On Sat, May 25, 2013 at 3:07 PM, atkaaz <atk...@gmail.com> wrote:
>>>>
>>>>> in which case it does get evaluated twice if form:
>>>>> => (pred-transform (println 1) #(not (nil? %)) #(println % "."))
>>>>> 1
>>>>> 1
>>>>> nil .
>>>>> nil
>>>>>
>>>>> => (pred-transform (println 1) nil? #(println % "."))
>>>>> 1
>>>>> 1
>>>>> nil
>>>>>
>>>>> so maybe a let + gensym would be in order?
>>>>>
>>>>>
>>>>>
>>>>> On Sat, May 25, 2013 at 3:04 PM, atkaaz <atk...@gmail.com> wrote:
>>>>>
>>>>>> Shouldn't it be like:
>>>>>>
>>>>>> (definline pred-transform [obj pred tf]
>>>>>> `(if (~pred ~obj) ~obj
>>>>>> (~tf ~obj)))
>>>>>> => (pred-transform 1 #(not (nil? %)) println)
>>>>>> 1
>>>>>> => (pred-transform 1 nil? println)
>>>>>> 1
>>>>>> nil
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Sat, May 25, 2013 at 2:55 PM, atkaaz <atk...@gmail.com> wrote:
>>>>>>
>>>>>>> just wondering if obj is a form does it get evaluated twice?
>>>>>>>
>>>>>>>
>>>>>>> On Sat, May 25, 2013 at 2:51 PM, Jim - FooBar(); <
>>>>>>> jimpil1...@gmail.com> wrote:
>>>>>>>
>>>>>>>> no need for macros... :)
>>>>>>>>
>>>>>>>> (definline safe-assoc [m k v]
>>>>>>>> `(if (contains? ~m ~k) ~m
>>>>>>>> (assoc ~m ~k ~v)))
>>>>>>>>
>>>>>>>> (definline pred-transform [obj pred tf]
>>>>>>>> `(if ~(pred obj) ~obj
>>>>>>>> ~(tf obj)))
>>>>>>>>
>>>>>>>> Jim
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On 25/05/13 12:44, atkaaz wrote:
>>>>>>>>
>>>>>>>> may I see the macro for the latter, if you decide to go that way ?
>>>>>>>> thx
>>>>>>>>
>>>>>>>>
>>>>>>>> On Sat, May 25, 2013 at 2:24 PM, Steven Degutis <
>>>>>>>> sbdegu...@gmail.com> wrote:
>>>>>>>>
>>>>>>>>> There are two patterns I find in my code that I'm still unhappy
>>>>>>>>> with but I don't know how to clean up.
>>>>>>>>>
>>>>>>>>> The first is: (if (:attr obj) obj (assoc obj :attr something))
>>>>>>>>>
>>>>>>>>> I'm basically saying, give this hash-map an attribute if it
>>>>>>>>> doesn't already have it. And just return the thing with an attribute,
>>>>>>>>> regardless if I had to add it or not.
>>>>>>>>>
>>>>>>>>> This version is ugly because it repeats obj three times. I could
>>>>>>>>> write my own macro to de-duplicate it, but I avoid doing that when I
>>>>>>>>> can
>>>>>>>>> because there's usually a better built-in solution that I just don't
>>>>>>>>> know
>>>>>>>>> about yet.
>>>>>>>>>
>>>>>>>>> The second is like it: (if (some-test obj) obj
>>>>>>>>> (some-transformation obj))
>>>>>>>>>
>>>>>>>>> In this one, I just want to return the object, but maybe
>>>>>>>>> transform it first. But the reference to obj happens three times!
>>>>>>>>> Still
>>>>>>>>> feels like it could be cleaned up.
>>>>>>>>>
>>>>>>>>> Any thoughts on how to clean these up?
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