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author | EuAndreh <eu@euandre.org> | 2021-04-24 15:31:39 -0300 |
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committer | EuAndreh <eu@euandre.org> | 2021-04-24 15:31:39 -0300 |
commit | 01efb4c06187c20e48585a1743c0a1708074aeac (patch) | |
tree | ebb0be96835578a38486be0964db51f6af492499 | |
parent | /home/andreh/dev/libre/dotfiles/scripts/pastebin.sh: Auto-add _pastebins/2021... (diff) | |
download | euandre.org-01efb4c06187c20e48585a1743c0a1708074aeac.tar.gz euandre.org-01efb4c06187c20e48585a1743c0a1708074aeac.tar.xz |
Add TIL on Clojure auto-currying
-rw-r--r-- | _tils/2021-04-24-clojure-auto-curry.md | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/_tils/2021-04-24-clojure-auto-curry.md b/_tils/2021-04-24-clojure-auto-curry.md new file mode 100644 index 0000000..8a54561 --- /dev/null +++ b/_tils/2021-04-24-clojure-auto-curry.md @@ -0,0 +1,74 @@ +--- + +title: Clojure auto curry + +date: 2021-04-24 + +layout: post + +lang: en + +ref: clojure-auto-curry + +--- + +A simple macro defined by [Loretta He][lorettahe] to create Clojure functions that are curried on all arguments, relying on Clojure's multi-arity support: + +```clojure +(defmacro defcurry + [fname args & body] + (let [partials (map (fn [n] + `(~(subvec args 0 n) (partial ~fname ~@(take n args)))) + (range 1 (count args)))] + `(defn ~fname + (~args ~@body) + ~@partials))) +``` + +A naive `add` definition, alongside its usage and macroexpansion: + +```clojure +user=> (defcurry add + [a b c d e] + (+ 1 2 3 4 5)) +#'user/add + +user=> (add 1) +#object[clojure.core$partial$fn__5857 0x2c708440 "clojure.core$partial$fn__5857@2c708440"] + +user=> (add 1 2 3 4) +#object[clojure.core$partial$fn__5863 0xf4c0e4e "clojure.core$partial$fn__5863@f4c0e4e"] + +user=> ((add 1) 2 3 4 5) +15 + +user=> (((add 1) 2 3) 4 5) +15 + +user=> (use 'clojure.pprint) +nil + +user=> (pprint + (macroexpand + '(defcurry add + [a b c d e] + (+ 1 2 3 4 5)))) +(def + add + (clojure.core/fn + ([a b c d e] (+ 1 2 3 4 5)) + ([a] (clojure.core/partial add a)) + ([a b] (clojure.core/partial add a b)) + ([a b c] (clojure.core/partial add a b c)) + ([a b c d] (clojure.core/partial add a b c d)))) +nil +``` + +This simplistic `defcurry` definition doesn't support optional parameters, multi-arity, `&` rest arguments, docstrings, etc., but it could certainly evolve to do so. + +I like how `defcurry` is so short, and abdicates the responsability of doing the multi-arity logic to Clojure's built-in multi-arity support. +Simple and elegant. + +Same Clojure as before, now with auto-currying via macros. + +[lorettahe]: http://lorettahe.github.io/clojure/2016/09/22/clojure-auto-curry |