Thanks Laurent and Jim — yes, fnil is what I was looking for.
On Friday, 5 April 2013 12:25:17 UTC+1, Simon Katz wrote:
>
> Hi.
>
> Is there an idiomatic way to have update-in create a vector when the
> supplied keys do not already exist? (Or maybe I should use something other
> than update-in?)
>
> For example...
>
> This gives me a sequence of things in the reverse of the order I want:
>
> (update-in {} [:foo :bar] conj :a)
> ;; => {:foo {:bar (:a)}}
>
> (update-in *1 [:foo :bar] conj :b)
> ;; => {:foo {:bar (:b :a)}}
>
> This does what I want, but at the expense of creating a new vector each
> time:
>
> (update-in {} [:foo :bar] (comp vec conj) :a)
> ;; => {:foo {:bar [:a]}}
>
> (update-in *1 [:foo :bar] (comp vec conj) :b)
> ;; => {:foo {:bar [:a :b]}}
>
> (I know about laziness and structure sharing, and that this expense may
> not be large.)
>
> The following works, but at the expense of a new function that the reader
> has to understand:
>
> (defn conj-vec
> "Like conj, but returns a vector if coll is empty.
> Useful in conjunction with update-in."
> [coll x]
> (if (empty? coll) [x] (conj coll x)))
>
> (update-in {} [:foo :bar] conj-vec :a)
> ;; => {:foo {:bar [:a]}}
>
> (update-in *1 [:foo :bar] conj-vec :b)
> ;; => {:foo {:bar [:a :b]}}
>
> Is there a better way?
>
--
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to clojure+unsubscr...@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
