@danielcompton: I don’t think so, since it’s still creating a seq.

@danburton: dirty Clojure trick

user=> (contains? [:a :b :c] :b)
false
user=> (.contains [:a :b :c] :b)
true

Hi clojurians! is there a way to invert the order of threading inside a ->> macro?

say, at a certain step I need the result of the previous to be taken as the first argument, not as the last. I often use #(function % var1 var2) in order to accomplish this, but I believe there has to be a more idiomatic way to do it

@vandr0iy: take a look at as->

thanks @codonnell

would relying on the fact that PersistentArrayMap retains the order of its keys be a really bad idea if I know my map will only ever contain 4 entries?

@luxbock: yeah I would not recommeng doing that

Although the Monger library does it

can't you use a sorted map?

@val_waeselynck: yes I could, but I'm serializing this data as EDN and sorted-maps don't work so well with that

I need to create a utility function to verify that a map contains a substructure, for example {:a "boo" :b{:d "hoo" :e "wam"} :c "bulance"} would have a substructures defined as {}, {:a #{} :c #{}}, {:b #{:d :e}}, among others

here is my implementation:

(defn has-substructure? [i s] (cond (nil? (not-empty s)) true (nil? (not-empty i)) false (map? s) (every? #(and (contains? i (key %)) (has-substructure? (get i (key %)) (val %))) s) (set? s) (every? #(contains? i %) s) :else false))

I am trying to figure out how to use the recur keyword instead, but it won't work as is because the macro #(...) expands to (fn ...) which intercepts the recur

@bcbradley: recur only works for tail-recursion

wouldn't this be tail recursion without the (every? ...)

without it yes 🙂

@bcbradley: tail recursion isn't really compatible with dividing the problem then combining the results

are you certain?

(nil? (not-empty s)) can be (empty? s)

thanks for that lux

i'm not really trying to "combine" results in a merge fashion

as soon as i can determine that the substructure is not met by the provided collection, i can return false

i suppose (not (some (not ... could replace (every?

but that doesn't fix the recur problem

i'm open to reworking the whole function if you can come up with a better way to do it

@bcbradley: http://lambda-startup.com/traversing-trees-tail-recursively/

I'll give it a look, but i know what tail recursion is. I'm just trying to figure out how to make my algorithm tail recursive

i don't want to use a trampoline unless i have to

@luxbock: not a bad idea if you construct the map via array-map and you're sure you're not going to conj/`dissoc` from it. it's documented behaviour

arraymaps and sorted-maps have different kinds of "ordering". arraymaps guarantee insertion order, sorted-maps guarantee ordering based on properties of the keys

@bronsa thanks

Hi can someone help me understand what's going on here. user=> (def var 42) #'user/var user=> (prn var (var var)) 42 #'user/var

What are you expecting it to do?

var is a special form

(var x) is the same as #'x

(var var) is the same as #'var

I'm wondering how Clojure resolves that

If only func-a needs to call func-b, func-c, and func-d, but func-c and func-d also need to call func-a, how would you organize that?

sounds like infinite recursion

Selective dispatch. Based on contents of supplied map, A calls one of B, C, or D on the map. C and D maps may contain further maps that need to be dispatched on, thus handing back to A. Tree-structure. Has a bottom.

@bpicolo: A (the dispatch function) needs to be called by some of the individual handlers because they may contain further nodes of the tree.

ah

The recursion is as infinite as an Emacs org-mode file.

Maybe let-fn

?

Ah. declare will do the job.