Specter – Clojure API for immutable programming (2017) • Hacker News Board

Specter – Clojure API for immutable programming (2017)

#1

Post by amgreg » Fri, Sep 04, 2020, 12:41 PM UTC

Specter – Clojure API for immutable programming (2017)
nathanmarz.com

Re: Specter – Clojure API for immutable programming (2017)

#2

Post by boxed » Fri, Sep 04, 2020, 2:34 PM UTC

I invented instar (https://github.com/boxed/Instar) which is quite similar to specter (imo a little bit nicer) because I also thought the built in API was weirdly clunky in these respects.

Re: Specter – Clojure API for immutable programming (2017)

#3

Post by john-shaffer » Fri, Sep 04, 2020, 2:45 PM UTC

Specter is fantastic. It makes transformations on deeply nested data structures easy. Want to transform all the "datetimes" from JSON data into actual datetimes (or vice versa)? It takes about five minutes if you have to look everything up. Works with ClojureScript too.

Some production code:

    (defn transform-tagged-values [x]
      (sp/transform (sp/walker tr/tagged-value?) tagged-value->cljs x))

Give it a predicate for which values to transform, and a function to do the transformation. Couldn't be easier.

Re: Specter – Clojure API for immutable programming (2017)

#4

Post by slifin » Fri, Sep 04, 2020, 2:59 PM UTC

There's a lot of alternatives in this space

Meander was the last one I can remember:

https://www.youtube.com/watch?v=9fhnJpCgtUw

Re: Specter – Clojure API for immutable programming (2017)

#5

Post by [deleted] » Fri, Sep 04, 2020, 3:32 PM UTC

slifin wrote: post #4

There's a lot of alternatives in this space Meander was the last one I can remember: https://www.youtube.com/watch?v=9fhnJpCgtUw

[deleted]

Re: Specter – Clojure API for immutable programming (2017)

#6

Post by tekacs » Fri, Sep 04, 2020, 3:37 PM UTC

Specter is tremendously useful and rarely lets on a case where it can’t perform a transformation. For ensuring that you’re getting the most efficient form of a transformation [0] it’s incredible —- and it is somewhat data-oriented, allowing easy saving and reuse of navigators.

Meander [1] is also wonderful. Its unification-based approach makes for nice expressions of intent. Its strategy-based approach to rewriting [2] is more flexible than most common walker libraries, too.

[0]: https://github.com/redplanetlabs/specter/wiki/Specter's-inli...

[1]: https://github.com/noprompt/meander

[2]: https://github.com/noprompt/meander/blob/epsilon/doc/strateg...

Re: Specter – Clojure API for immutable programming (2017)

#7

Post by jdc » Fri, Sep 04, 2020, 4:25 PM UTC

Previous discussion of Specter: https://news.ycombinator.com/item?id=10295060

also cf

Glom for Python: https://sedimental.org/glom_restructured_data.html

Hashdig in Ruby's standard library: https://ruby-doc.org/core-2.7.1/Hash.html#method-i-dig

Re: Specter – Clojure API for immutable programming (2017)

#8

Post by sova » Fri, Sep 04, 2020, 5:03 PM UTC

Like SQL for nested maps in Clojureland. Neat. The DSL [ALL :a even?] does feel a tiny bit un-clojurey to me as well, maybe making it look like [:all :a even?] would make it clearer.

Re: Specter – Clojure API for immutable programming (2017)

#9

Post by escherize » Fri, Sep 04, 2020, 5:07 PM UTC

sova wrote: post #8

Like SQL for nested maps in Clojureland. Neat. The DSL [ALL :a even?] does feel a tiny bit un-clojurey to me as well, maybe making it look like [:all :a even?] would make it clearer.

Well, not sure about that exactly. Consider a map like:

    {:all {:a 2} :foo {:a 4}}

Maybe namespaced keys would fit that usecase

Re: Specter – Clojure API for immutable programming (2017)

#10

Post by didibus » Fri, Sep 04, 2020, 5:55 PM UTC

boxed wrote: post #2

I invented instar ( https://github.com/boxed/Instar ) which is quite similar to specter (imo a little bit nicer) because I also thought the built in API was weirdly clunky in these respects.

What's the performance vis-a-vis Specter?