[ANN] Specter 0.9.2

[Nathan Marz]

I just released Specter 0.9.2:

https://github.com/nathanmarz/specter

https://clojars.org/com.rpl/specter/versions/0.9.2

Specter solves a near-universal problem encountered when writing Clojure/ClojureScript: the need to transform or query a data structure that's more sophisticated than a basic map or list. It is a library that captures the notion of "navigation" within a data structure and allows for writing elegant queries and transformations. Its performance is close to hand-optimized code so it can be used even in performance-critical code. Additionally, Specter is extensible to any data structure as it is based on a simple protocol.

There have been over 15 releases since I last posted about Specter on the group (almost a year ago), and there's been a ton of improvements since then:

- Precompilation feature enabling performance rivaling hand-optimized code

- Facilities for creating recursive navigators, including pre-walk and post-walk traversals (declarepath/providepath, stay-then-continue, continue-then-stay)

- ClojureScript support

- Conditional navigation (if-path, cond-path)

- Protocol paths: navigate based on the type of data encountered

- "Batteries included" set of navigators that captures majority of use cases dealing with combinations of maps, lists, vectors, and sets

[Jean Baro]

Congratulations for the spectacular work and thanks for sharing this with the world.

[Alan Thompson]

Looks great, Nathan.  I also highly enjoyed your recent interview on the Cognitect podcast .   

One quick question:  In the first example below from the README (verified at the repl), it seems that the (srange ...) function sometimes behaves as a half-open interval [1,4) like the (range ...) function in Clojure).  However, in the 2nd example it seems to behave as a closed interval [2,4].  Is there an easy way of knowing which behavior applies in different situations?

Thanks, 

Alan

Here's how to increment all the odd numbers between indexes 1 (inclusive) and 4 (exclusive):

user> (transform [(srange 1 4) ALL odd?] inc [0 1 2 3 4 5 6 7])

[0 2 2 4 4 5 6 7]

Here's how to replace the subsequence from index 2 to 4 with [-1 -1 -1]:

user> (setval (srange 2 4) [-1 -1 -1] [0 1 2 3 4 5 6 7 8 9])

[0 1 -1 -1 -1 4 5 6 7 8 9]

On Thu, Jan 28, 2016 at 4:11 PM, Jean Baro <jfb...@gmail.com> wrote:

Congratulations for the spectacular work and thanks for sharing this with the world.

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[Nathan Marz]

Both of those examples use half-open intervals :) The first selects the subsequence with indices 1,2,3, and the second selects the subsequence with indices 2,3. You can see in the second example that [2 3] in the overall sequence is replaced by [-1 -1 -1].

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[Alan Thompson]

Oh!  I never even suspected that!  So you are replacing a length-2 subsequence with a length-3 subsequence.  Very flexible.

It might be useful to point out that feature in the docs.   :)

Alan

[Nathan Marz]

I updated the example with a larger replacement sequence to hopefully prevent that confusion in the future.

You can also use srange to eliminate subsequences, e.g.:

(setval (srange 4 7) nil [:a :b :c :d :e :f :g :h :i])

=> [:a :b :c :d :h :i]

And the navigator to prepend to a sequence is just selecting the empty subsequence at the beginning:

(def BEGINNING (srange 0 0))

(setval BEGINNING [:a :b] '(1 2 3))

=> (:a :b 1 2 3)

[Alan Thompson]

nice.

[Jason Lewis]

Wow, I hadn't seen this lib before, it really *is* the missing piece in a lot of ways. 

One question, are you considering migrating from cljx to cljc for cross-compiling? We've been trying to eliminate cljx dependencies in favor of cljc, and I'd be happy to help with the effort if it's on the roadmap.

cheers,

Jason

[Nathan Marz]

It used to use cljc but needed to switch to cljx so that it could be compatible with Clojure 1.6. It doesn't really affect users, it just adds some inconvenience to working on Specter itself. Once it looks like most people are on 1.7 or above, I'm all for switching it back to cljc. 

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