Hi.
I'm new to clojure, and it is quite lovely. The threading model is great,
the emacs integration is super, and the tasteful lisp extensions are good.
A very nice programming environment all around.
But as I write more code I find a couple of structures I'm using a lot
which seem related to me not knowing idioms for a couple of uses cases. So
thought I'd ask and see if you have any suggestions.
Apologies if this is covered elsewhere. And if I should read some existing
documentation I didn't find, I apologize for missing it. And thanks in
advance for your time reading!
First the thrush operators (-> and ->>) are super handy. But I find myself
needing to 'move' arguments every now and then. So I get code which looks
like
(->> blah
(do-this)
(do-that arg)
((fn [s] (rearrange arg s arg))))
quite a lot.The alternate is a big nested let like
(let [ first (blah)
second (do-this first)
...
result (wrap-it-up fourteenth) ]
result)
for sort of sequential application where arguments fall in different
'spots'. So I sort of find myself wanting to write a 'positional-thrush'
macro like
(-%> blah
(do-this %)
(do-that arg %)
(do-the-other a1 % a2))
where % is replaced with the output of the prior. But no such operator
exists as far as I can see. So either I've had a good idea (which is
unlikely since I'm super new to the language) or there's some other idiom
you all use for this pattern which I've missed.
The second is smaller, but is more a question. clojure.test seems to only
have 'is' so for things like equality I end up writing (is (= (...) (...)))
a lot. Or to test if an exception is thrown (is (thrown? ...)). That's OK,
but I'm wondering what led to that decision rather than having is-eq and
is-thrown and so on (considering the core language has shortcuts like when
and unless and if-not so the compound macros seem idiomatic).
The last is sort of related to the first. Sometimes I'm assembling a data
structure in a set of operators and I write them with a let or a -> and
half way through I have an error condition I want to check. In a mutable
procedural language you would do something like
x = blah
y = bim
if (! (condition (y))) throw "y doesn't meet condition"
z = blob
I don't see a good idiom for this. I have to split and nest lets for
instance
(let [x (blah) y (bim) ]
(if (condition (y)) (throw ...)
(let [ z (blob) ]
))
which seems a bit ugly. I sort of want a let-with-test or a
thrush-with-test so something which looks like
(-%?> (init)
(operator-1 %) (post-condition)
(operator-2 %) (post-condition) )
where if I don't have a post condition I could just use 'true'. Then this
expands to doing a quick '(if (not (postcondition (intermedia-result))))
throw...)
but that's a crazy thing to want. So curious how you all tackle this.
Thank you all for your consideration. And apologies again if this is
covered elsewhere or I should have asked in a different forum.
Best,
Paul
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