Hacker News Reader

Hacker News

Comment by intertextuality | Hacker News Reader

Parent Full thread

intertextuality

Clojure does indeed have -> (thread-first), ->> (thread-last), some->, some->>, cond->, and as->. [0]

(->) inserts each form's value between the function name & the first argument in the next form.

(->>) inserts each form's value as the last argument in the next form.

The latter forms are much more niche and I haven't found need for them yet.

[0]: https://clojure.org/guides/threading_macros

View on HN

Bucklescript/ReasonML have that too:

CLJ:(->)/BS(|.)/RML(->) called Fast Pipe.

CLJ:(->>)/BS(|>)/RML(|>) called Pipe.

plus some nifty placeholders for other positions:

https://reasonml.github.io/docs/en/fast-pipe#pipe-placeholde...

as-> is great for when you have to mix thread-first and thread-last.

cond-> is great for building maps where some keys might not be needed:

    (cond-> {:k1 v1}
      v2 (assoc :k2 v2)
      ...)

some-> and some->> I don't use as often, but when mixing in some java code that could throw an NPE, these will avoid that and just return nil early (they short-circuit when getting a nil value).

You can next ->> inside ->, took far too many years for me to realize:

    @(-> ctx
        :hypercrud.browser/fiddle
        (reactive/cursor [:fiddle/ident])
        (->> (reactive/fmap name)))

another

    (-> [10 11] 
        (conj 12) 
        (as-> xs (map - xs [3 2 1])) 
        (reverse))

Reply on news.ycombinator.com