Tips for golfing in Clojure

Question

What are your tips for code golfing using Clojure?

The aim of this question is to collect a list of techniques that are specific to Clojure and can be used in general code-golfing problems.

Answer 1

Use reader syntax for lambdas.
So use

#(+ % %2 %3)

instead of

(fn [x y z] (+ x y z))

You can also eliminate whitespace some of the time:

#(if (< % 0) (- %) %)
#(if(< % 0)(- %)%)

Answer 2

Where you can remove whitespace:

• Between a string and anything else:

  (println(+"Hello, World!"1))
  

• Between brackets and anything else:

  (for[x(range 5)](* x x))
  

• Between a number and everything other than builtins or variable names:

  Allowed:
  (+ 1"Example")
  (map{1"-1"2"-2"}[1 2 3])
  
  Not allowed:
  (+1 2)
  

• Between @ (dereference for atoms) and brackets.

Answer 3

Strings can be treated as a sequence of chars

e.g. to sort the characters in a string alphabetically:

(sort "hello")
=> (\e \h \l \l \o)

Answer 4

Use nth ... 0 instead of first

To get the first element of a collection, using (nth ... 0) over first saves a byte:

(first[2 3 4]): 14 bytes
(nth[2 3 4]0): 13 bytes (saves a byte!)

Answer 5

Use apply instead of reduce

For example #(apply + %) is one byte shorter than #(reduce + %).

Answer 6

Bind long function names at let to a single-byte symbol

For example if you need to use partition or frequencies multiple times, it could be beneficial to bind them to a single-byte symbol in a let macro. Then again it might not be worth it if you don't need the let otherwise, and the function name is relatively short.

Answer 7

Avoid let if you already have a for

For example: #(for[a[(sort %)]...) instead of #(let[a(sort %)](for ...)).

For does also have a :let construct but it is too verbose for code golf.

Answer 8

Use + and - instead of inc and dec

This saves 1 byte if you're using inc/dec on an expression with parens:

(inc(first[1 3 5]))
(+(first[1 3 5])1)

Answer 9

Use maps instead of ifs when testing for equality

;; if n=3 then A else B
(if (= 3 n) A B) ; (if(=3n)AB)
({3 A} n B)      ; ({3A}nB) -> -3 chars

;; if n=2 or n=3 then A else B
(if (#{2 3} n) A B) ; (if(#{23}n)AB)
({2 A 3 A} n B)     ; ({2A3A}nB) -> -4 chars

Answer 10

Use for instead of map

For instance #(for[i %](Math/abs i)) is a lot shorter than the map equvalent.