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---
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
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