JavaScript Curry

ba-curry.js

/*!
 * JavaScript Curry - v0.1pre - 11/29/2010
 * http://benalman.com/
 * 
 * Copyright (c) 2010 "Cowboy" Ben Alman
 * Dual licensed under the MIT and GPL licenses.
 * http://benalman.com/about/license/
 */

function curry(/* n,*/ fn /*, args...*/) {
  var n,
    aps = Array.prototype.slice,
    orig_args = aps.call( arguments, 1 );
  
  if ( typeof fn === 'number' ) {
    n = fn;
    fn = orig_args.shift();
  } else {
    n = fn.length;
  }
  
  return function() {
    var args = orig_args.concat( aps.call( arguments ) );
    
    return args.length < n
      ? curry.apply( this, [ n, fn ].concat( args ) )
      : fn.apply( this, args );
  };
}

/*

var i = 0;
function a( x, y, z ) {
  console.log( ++i + ': ' + x + ' and ' + y + ' or ' + z );
};

a( 'x', 'y', 'z' );     // "1: x and y or z"

var b = curry( a );
b();                    // nothing logged, `a` not invoked
b( 'x' );               // nothing logged, `a` not invoked
b( 'x', 'y' );          // nothing logged, `a` not invoked
b( 'x' )( 'y' );        // nothing logged, `a` not invoked
b( 'x' )( 'y' )( 'z' ); // "2: x and y or z"
b( 'x', 'y', 'z' );     // "3: x and y or z"

var c = curry( a, 'x' );
c();                    // nothing logged, `a` not invoked
c( 'y' );               // nothing logged, `a` not invoked
c( 'y', 'z' );          // "4: x and y or z"
c( 'y' )( 'z' );        // "5: x and y or z"

var d = curry( c, 'y' );
d();                    // nothing logged, `c` not invoked
d( 'z' );               // "6: x and y or z"

var e = curry( a, 'x', 'y' );
e();                    // nothing logged, `a` not invoked
e( 'z' );               // "7: x and y or z"

var f = curry( a, 'x', 'y', 'z' );
f();                    // "8: x and y or z"

var g = curry( a )( 'x' );
g();                    // nothing logged, `a` not invoked
g( 'y' );               // nothing logged, `a` not invoked
g( 'y', 'z' );          // "9: x and y or z"
g( 'y' )( 'z' );        // "10: x and y or z"

var h = curry( a, 'x' )( 'y' );
h();                    // nothing logged, `a` not invoked
h( 'z' );               // "11: x and y or z"


function aNoLength() {
  var x = arguments[0], y = arguments[1], z = arguments[2];
  console.log( ++i + ': ' + x + ' and ' + y + ' or ' + z );
};

// You must specify `n` of 3 here since aNoLength.length == 0!

var j = curry( 3, aNoLength );
j();                    // nothing logged, `aNoLength` not invoked
j( 'x' );               // nothing logged, `aNoLength` not invoked
j( 'x', 'y' );          // nothing logged, `aNoLength` not invoked
j( 'x' )( 'y' );        // nothing logged, `aNoLength` not invoked
j( 'x' )( 'y' )( 'z' ); // "12: x and y or z"
j( 'x', 'y', 'z' );     // "13: x and y or z"

// And BTW, because the unsatisfied curried function continues to
// return a function, invoking that function without arguments
// keeps returning a function. So have fun!
j()()()( 'x' )()()()( 'y' )()()()( 'z' ); // "14: x and y or z"
j()()()()()( 'x', 'y' )()()()()()( 'z' ); // "15: x and y or z"
j()()()()()()()()()()()( 'x', 'y', 'z' ); // "16: x and y or z"

*/

Array.prototype.slice creates shallow copies only, so be wary of working on object arguments as it will retain a pointer to the original object (as opposed to working on strings or numbers).

This behavior is consistent with how object arguments are passed into any JavaScript function, which is to say, by reference. Object copying in any currying or partial application context doesn't make sense.