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Programming-Idioms

  • Haskell
  • Clojure

Idiom #37 Currying

Transform a function that takes multiple arguments into a function for which some of the arguments are preset.

(def add5 (partial + 5))
(def rev-key #(update %2 %1 reverse))

(def rev-a (partial rev-key :a))

addThem :: Num a => a -> a -> a
addThem = (+)

add5 :: Num a => a -> a
add5 = addThem 5
import Data.Ix
curry range

range(a,b) = [a..b]
(curry range 1) = \ i -> [1..i]
curry range :: a -> a -> [a]
curry :: ((a, b) -> c) -> a -> b -> c
"::" means "is of type"

Haskell begins with most functions already curried and allowing partial projection, hence the uncurried range sprang to mind as a notable exception for this illustration.

Data.Ix contains range
//function
auto add(int a, int b) -> int {
	return a + b;
}

//curry with std::bind
using namespace std::placeholders;
auto add5 = std::bind(add, _1, 5);

//curry with lambda
auto add5 = [](int x) { return add(x, 5); };

//use
auto result = add5(1);
assert(result == 6);

You can use std::bind or a lambda to do so.
New implementation...
< > ⌨
Adrian 
(def add5 (partial + 5))
(def rev-key #(update %2 %1 reverse))

(def rev-a (partial rev-key :a))

addThem :: Num a => a -> a -> a
addThem = (+)

add5 :: Num a => a -> a
add5 = addThem 5
curry range

//function
auto add(int a, int b) -> int {
	return a + b;
}

//curry with std::bind
using namespace std::placeholders;
auto add5 = std::bind(add, _1, 5);

//curry with lambda
auto add5 = [](int x) { return add(x, 5); };

//use
auto result = add5(1);
assert(result == 6);
// function taking many parameters
int add(int a, int b)
{
    return a + b;
}

// define a new function preseting the first parameter
std::function<int (int)> add_def(int a)
{
    return [a](int b){return add(a, b);};
}

int result = add_def(4)(6);
Func<A, C> curry<A, B, C>(Func<A, B, C> f, B b) => (A a) => f(a, b);
int add(int n1, int n2)
{
    return n1 + n2;
}

alias add5 = curry!(add, 5);
curry(f(a, b), a) => (b) => f(a, b);
defmodule Curry do

  def curry(fun) do
    {_, arity} = :erlang.fun_info(fun, :arity)
    curry(fun, arity, [])
  end

  def curry(fun, 0, arguments) do
    apply(fun, Enum.reverse arguments)
  end

  def curry(fun, arity, arguments) do
    fn arg -> curry(fun, arity - 1, [arg | arguments]) end
  end

end
type PayFactory func(Company, *Employee, *Employee) Payroll

type CustomPayFactory func(*Employee) Payroll

func CurryPayFactory(pf PayFactory,company Company, boss *Employee) CustomPayFactory {
	return func(e *Employee) Payroll {
		return pf(company, boss, e)
	}
}
function curry (fn, scope) {
   
    scope = scope || window;
    
    // omit curry function first arguments fn and scope
    var args = Array.prototype.slice.call(arguments, 2);
    
    return function() {
	var trueArgs = args.concat(Array.prototype.slice.call(arguments, 0));
        fn.apply(scope, trueArgs);
    };
}
const curry = (fn, ...initialArgs) => (...args) => fn(...initialArgs, ...args);

const add = (a, b) => a + b;

const add5 = curry(add, 5);

const result = add5(1) // 6
IntBinaryOperator simpleAdd = (a, b) -> a + b;
IntFunction<IntUnaryOperator> curriedAdd = a -> b -> a + b;
System.out.println(simpleAdd.applyAsInt(4, 5));
System.out.println(curriedAdd.apply(4).applyAsInt(5));
(defun curry (fn &rest args)
  (lambda (&rest remaining-args)
    (apply fn (append args remaining-args))))

(defun add (a b)
  (+ a b))

(funcall (curry add 2) 1) 
  
function curry2(f)
   return function(a)
      return function(b)
         return f(a,b)
      end
   end
end

function add(a,b)
   return a + b
end

local curryAdd = curry2(add)
local add2 = curryAdd(2)
local unpack = unpack or table.unpack
local function aux_ncurry(n, m, fn, args)
  if m>n then return fn(unpack(args,1,n))end
  local new_args, new_m = {}, m
  for i=1,m-1 do new_args[i]=args[i]end
  return function(a) 
    new_args[new_m]=a
    return aux_ncurry(n, new_m + 1, fn, new_args)
  end
end
local function ncurry(n, fn) return aux_ncurry(n,1,fn,{}) end
function curry($f, ...$argsCurried)
{
    return function (...$args) use ($f, $argsCurried) {
        $finalArgs = array_merge($argsCurried, $args);
        return call_user_func_array($f, $finalArgs);
    };
}

function add($n1, $n2)
{
    return $n1 + $n2;
}

$addFive = curry('add', 5);

echo $addFive(2), PHP_EOL;
echo $addFive(-5), PHP_EOL;
function curry($f, ...$argsCurried)
{
    return function (...$args) use ($f, $argsCurried) {
        return $f(...$argsCurried, ...$args);
    };
}

function add($n1, $n2)
{
    return $n1 + $n2;
}

$addFive = curry('add', 5);

echo $addFive(2), PHP_EOL;
echo $addFive(-5), PHP_EOL;
sub curry {
   my ($func, $fixed_arg) = @_;
   return sub {
      $func->($fixed_arg, @_);
   }
}

def add(a, b):
	return a+b

add_to_two = partial(add, 2)
adder = -> a, b { a + b }
add_two = adder.curry.(2)
add_two.(5) # => 7
fn add(a: u32, b: u32) -> u32 {
    a + b
}

let add5 = move |x| add(5, x);
 
def add(x: Int)(y: Int) = x + y
val add5 = add(5)_
def add(x: Int, y: Int) = x + y
def add5 = add(5, _)
val seven = add5(2)
(define add5 (curry + 5))