If the condition is true of the transformed object (e.g., it's "if this
condition isn't met, use this method to massage it so it is"), then there's
this:
(first (filter condition? (map #(%1 obj) [identity transformation])))
It can even use laziness to avoid the transformation, but you'll need (list
identity transformation) instead of [identity transformation] to avoid
chunking the seq.
And it can then be extended with successively more-expensive
transformations that it will try until one makes condition? true of its
output.
On Sat, May 25, 2013 at 8:35 AM, Chris Ford <christophertf...@gmail.com>wrote:
> 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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