The primary point of let-> is that you can insert it into an existing ->
pipeline.
(-> foo
(stuff)
(blah)
(let-> foo-with-stuff
(for [x foo-with-stuff]
(inc x)))
Your proposal breaks this.
On Thursday, November 15, 2012 10:35:59 AM UTC-8, Alex Nixon wrote:
>
> Hi all,
>
> I find the proposed function let-> in Clojure 1.5 very useful, but a bit
> ugly. The arguments are backwards when compared to vanilla let, and it
> doesn't support destructuring where it easily could (which I believe would
> be helpful when threading 'state-like' maps, as I find let-> very useful
> for).
>
> I'd like to float an alternative implementation which improves on both
> these issues. Thoughts?
>
> (defmacro new-let->
> "Establishes bindings as provided for let, evaluates the first form
> in the lexical context of that binding, then re-establishes bindings
> to that result, repeating for each successive form"
> [bindings & forms]
> (assert (vector? bindings) "binding must be a vector")
> (assert (= 2 (count bindings)) "binding vector must contain exactly two
> forms")
> `(let [~@bindings
> ~@(interleave (repeat (bindings 0)) (drop-last forms))]
> ~(last forms)))
>
> (new-let-> [{:keys [foo bar] :as state} {:foo 1 :bar 2}]
> (assoc state :foo (inc bar))
> (assoc state :bar (inc foo))) ; => {:foo 3, :bar 4}
>
> --
> *Alex Nixon*
>
> Software Engineer | SwiftKey
>
> *[email protected] <javascript:>** | http://www.swiftkey.net/*
>
> ++++++
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>
>
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