Re: calling a clojure function within a quote/(')

[Dustin Getz]

Here is my attempt at gymnastics, exploits that < does indeed resolve to 
clojure.core/< in datomic query:

(def c 5)
[:find '?e :where ['?e :db/ident] [`(< ~'?e ~c)]]=> [:find 
?e :where [?e :db/ident] [(clojure.core/< ?e 5)]]
(d/q [:find '?e :where
  ['?e :db/ident]
  [`(< ~'?e ~c)]]
 $)
  => #{[1] [2] [3] [4] [0]}

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Re: calling a clojure function within a quote/(')

[Dustin Getz]

I wouldn't try to fight this battle, just parameterize the query

[:find ?e :in $ ?three :where
 [? :data/number ?number] 
 [(> ?number ?three)]]

http://docs.datomic.com/best-practices.html#parameterize-queries

*Datomic will cache queries, so long as the query (first) argument data 
structures evaluate as equal. As a result, reusing parameterized queries is 
much more efficient than building different query data structures. If you 
need to build data structures at run time for query, you should do so using 
a standard process so that equivalent queries will evaluate as equal.*

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Re: Map Keys are functions, why not vector elements?

[Alex Baranosky]

Practically speaking, Java numbers cannot be extended with the IFn
interface to make this possible.

On Mon, Nov 13, 2017 at 9:15 AM, Alex Miller  wrote:

> Regarding the title, this is incorrect. Map keys are not functions;
> keywords are functions that take an associative data structure and will
> look themselves up in it. So, the premise here is not even correct to start.
>
> Usually we prefer to work by starting from a problem and consider
> alternatives, but as you state below, you don't have a problem in mind.
>
>
> On Monday, November 13, 2017 at 3:49:41 AM UTC-6, Stephen Feyrer wrote:
>>
>> Hi there,
>>
>> This is possibly a silly question (and may have been asked before but I
>> couldn't find earlier examples) so here it goes.
>>
>> We start with a form which we're all familiar with:
>>
>> user=> (:this {:this "is" :the "same"})
>> "is"
>>
>>
>> Then it's not a stretch to go to:
>>
>> user=> (def the 1)
>> #'user/the
>> user=> (nth [1 "is" the :same] 1)
>>
>> "is"
>>
>>
>> Here's where it gets tricky as we enter the land of make believe and
>> what-if?
>>
>> I suggest a special form where vector elements could be treated like
>> functions in a manner similar to maps keys.  As this is purely
>> hypothetical there might be better ways of representing this:
>>
>> Get the nth element of the vector
>>
>> user=> (3 [1 "is" the :same])
>> :same
>>
>>
>>
> Note that you can do something similar now with:
>
> ([1 "is" the :same] 3)
>
> Whereas in the situation with maps, keywords (a specific common key type)
> are functions, here you are implying that anything could implicitly be
> invokable as a lookup function on an associative data structure. This
> doesn't make a lot of sense to me and would undoubtedly have performance
> effects. Maybe there is some case like `(map 1 [[:a 0] [:b 1] [:c 2]])`
> where this would make sense. But this doesn't make sense for all indexed
> data structures, just those indexed by longs. Layering invocability on
> longs would require special handling in the compiler (Keywords are a type
> that embeds this by implementing IFn naturally, so it's not a special case).
>
>
>> Get the nth element of the vector
>>
>> user=> (2 [1 "is" the :same])
>> 1
>>
>>
>> Get the nthiness of an element in the vector
>>
>> user=> (::same [1 "is" the :same])
>> 3
>>
>>
> This is something completely different - a linear search for a match.
> Clojure has considered and rejected making linear searching easier multiple
> times. It's almost always a sign that you are using the wrong data
> structure in the first place and should be using a hashed data structure
> instead. There is no chance we would do something like this.
>
>
>>
>> Get the nthiness of an element in the vector
>>
>> user=> (:the [1 "is" the :same])
>> 2
>>
>>
>> Get the nthiness of an element in the vector
>>
>> user=> (:1 [1 "is" the :same])
>> (0 2)
>>
>>
> I don't even understand what is intended here.
>
>
>> Taking things further into the realms of really you should have stopped
>> there!
>>
>> Get the these element of the vector
>>
>> user=> ((1 3) [1 "is" the :same])
>> ("is" :same)
>>
>>
>> Just for fun I tried:
>>
>> user=> ((:this :the) {:this "is" :the "same"})
>>
>>
>>
>> NullPointerException   user/eval786 (NO_SOURCE_FILE:1)
>>
>>
>>
>> I may be barking up the wrong tree or possibly just barking...  I hope
>> what I'm asking makes some sort of sense.
>>
>
> Not particularly.
>
>
>> By way of apology to the reader, when I began writing this question it
>> was ill thought out and seemed a lot simpler.  As a disclaimer, I can't
>> think of direct examples how this would improve readability or such or even
>> necessarily be useful.
>>
>
> Seems like that should have been a sign. :)
>
>
>> Though, that being said, I do believe that there people who'd make good
>> use of such a feature, though I don't know who they are either but I'm
>> hoping you're reading this ;)
>>
>> My parting shot, I have a guess as to why things are the way they are but
>> that is completely in substantiated and lacks in even the most basic
>> rationality as I also guess as to why my guess might not be true... :(
>>
>>
>> --
>> Warning!  If you question everything the answer you'll get is
>> "EVERYTHING!"
>>
>> Stephen.
>>
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Re: calling a clojure function within a quote/(')

[Alex Baranosky]

Also:

(cond-> query
true
(conj ['? :data/number '?number])
true
(conj [(list '> '?number (foo 2))]))

;; => [:find ?e :in $ :where w [? :data/number ?number] [(> ?number 3)]]

On Fri, Nov 17, 2017 at 8:44 PM, Matching Socks 
wrote:

> In the docs: "syntax quote" on https://clojure.org/reference/reader
>
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