Thanks, that solution's pretty great, although you're right about the
side-effects problem, so I can't always use this solution.
Also I just remembered, sometimes to solve the second one, I would do ((if
condition transformer identity) obj) but that feels ugly.
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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>>>>>
>>>>>
>>>>
>>>
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