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 <[email protected]> wrote:
> just wondering if obj is a form does it get evaluated twice?
>
>
> On Sat, May 25, 2013 at 2:51 PM, Jim - FooBar(); <[email protected]>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 <[email protected]>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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