@nathanmarz shall I create a github issue for the reducible traverse idea?

@aengelberg yea

done

Do I have to do something special use specter from cljs? I have [com.rpl/specter "0.11.1"] in my build.boot (set-env! :dependencies), but my :require [com.rpl.specter :refer [select]] fails with "Referred var com.rpl.specter/select does not exist"

@mac the core select/transform/etc. operations are macros now in com.rpl.specter.macros namespace

that was a change in 0.11.0

Ah, got it.

I get a ton of warnings about "Use of undeclared Var com.rpl.specter.impl/compiled-select*" just from using select.

@nathanmarz: I just added (:require-macros [com.rpl.specter.macros :as sp]) to my namespace.

are you also requiring com.rpl.specter namespace?

nathanmarz: no, is that the issue?

could be

nathanmarz: that fixed it 🙂

cool

nathanmarz: thanks, specter is a fantastic piece of kit.

thanks

@nathanmarz: when would you use continue-then-stay, vs stay-then-continue.

the first is pre-order traversal, the 2nd is post-order

in that tree example continue-then-stay would visit the leaves first

I’m just trying to think of an example problem, and how that might affect composition

if you're changing the structure of the tree itself it can change the result

post-order that adds children will not visit the children in the same navigation, pre-order will

Inside a recursive navigation path that was visiting every element in a tree this is irrelevant though

I’m just trying to imagine step by step what specter is returning. Is it possible with a continue-then-stay to collect-one from all the leaves of a tree

sort of, get the path from each leaf to the root node?

got it

@conaw you figured out how to do it?

well, figured out when I might use pre-order and post-order in a select I’m not totally sure how to do the transform though

Is there a way to use setval and just set the val of a particular submap to the values collected

you need to use transform for that

setval ignores value collection

gotcha, is it possible to use VAL or collect-one inside of continue-then-stay

I keep getting an arity error or nil values

show me the code

(transform [ALL (sp/continue-then-stay :children ALL (collect-one :node)) :parents] 
         (fn [& xs] (vector xs))   samplemap)

multiple arities passed to next-fn

or rather, wrong number of args(2) passed

oh

that's the only known bug in specter

https://github.com/nathanmarz/specter/issues/64

lol

continue-then-stay is a wrapper on multi-path then

yea

same is true for any of the higher order navigators

like if-path

cool

Also, you mentioned at Clojure/West a few exercises that you thought were good for figuring out how to write navigators or paths well. I think you said something about nested vectors of maps. I’m trying to put together a sort of 4clojurey set of challenges for someone learning specter, if you (or anyone else in this room) have any sample problems I’d love them

my favorite exercise (spoiler alert, it can only be elegantly solved with subselect) is:

;; given a vector of vectors, reverse all numbers without changing the length of any vector
in:  [[1 2 3] [4 5] [6] [7] [8 9 10]]
out: [[10 9 8] [7 6] [5] [4] [3 2 1]]

love it

hey that is quite elegant

🙂

here's another one: concatenate all continuous sequences of strings together

["hello" " " "word" 1 2 "a" "b" 3] -> ["hello word" 1 2 "ab" 3]

srange-dynamic?

continuous-subseqs

filterer

adding an element to a nested set (or creating the set if it doesn't exist) without defining any new functions (anonymous or not)

{:a #{1}} -> {:a #{1 2}}

in a sequence of maps, set the :b key to true if the value for :a exists and is greater than 10

[{:a 1} {:a 11 :c 1} {:d 4}] -> [{:a 1} {:a 11 :b true :c 1} {:d 4}]

gotta admit I’m a little stumped by what I got back from the continuous subsequence stuff

its navigating to each character?

(transform [(sp/continuous-subseqs string?)] str ["hello " "a " "w" 1 2 3 "a " "b" ]) [\[ \" \h \e \l \l \o \space \" \space \" \a \space \" \space \" \w \" \] 1 2 3 \[ \" \a \space \" \space \" \b \" \]]

the transform fn gets sequence in and expects sequence out

so the challenge isn’t in the path, but in the fn you pass to transform

you're turning a vector of strings into a big string, which is then spliced back in as a sequence

yea, it's just understanding how the navigation works

gotcha, to do this well you’d really have to do something after the transform fn

your path is right and the rest of it is making a different transform-fn

your transform-fn will be called twice, once with ["hello " "a " "w"] and once with ["a " "b"]

Yeah, this is a good one, because I’m definitely failing to understand something about specter

(s/def ::stringvec (s/+ (s/spec (s/+  string?))))



(defn joinup [stringvec]
  (map (partial str/join "") stringvec))


(s/fdef joinup :args ::stringvec
        :ret string?)

(s/instrument 'joinup)

(transform [(sp/continuous-subseqs string?)] joinup
            ["hello " "a " "w" 1 2 3 "a " "b" ])

still getting back this ["hello " "a " "w" 1 2 3 "a " "b"]

yet the spec says I’m returning a string

here i'll show you

(fn [strseq] [(apply str strseq)])

so, because I’m not putting it in a vector at the end

what’s happening

?

continuous-subseqs works just like srange

the sequence returned back replaces the subsequence navigated to

so if you just return a string back, that gets interpreted as a sequence and the individual characters get spliced in

gotchaaa

yeah, that’s totally obvious when you think about it

yea, you just need to visualize it

truth, any challenges that involve navigating to a non-empty subset

I could imagine minecraft style ones

for sequence of players, if :inventory contains :flint and :stick, replace with :torch