var _curry1 = require('./internal/_curry1');
var nAry = require('./nAry');


/**
 * Wraps a function of any arity (including nullary) in a function that accepts
 * exactly 2 parameters. Any extraneous parameters will not be passed to the
 * supplied function.
 *
 * @func
 * @memberOf R
 * @since v0.2.0
 * @category Function
 * @sig (* -> c) -> (a, b -> c)
 * @param {Function} fn The function to wrap.
 * @return {Function} A new function wrapping `fn`. The new function is guaranteed to be of
 *         arity 2.
 * @see R.nAry, R.unary
 * @example
 *
 *      var takesThreeArgs = function(a, b, c) {
 *        return [a, b, c];
 *      };
 *      takesThreeArgs.length; //=> 3
 *      takesThreeArgs(1, 2, 3); //=> [1, 2, 3]
 *
 *      var takesTwoArgs = R.binary(takesThreeArgs);
 *      takesTwoArgs.length; //=> 2
 *      // Only 2 arguments are passed to the wrapped function
 *      takesTwoArgs(1, 2, 3); //=> [1, 2, undefined]
 * @symb R.binary(f)(a, b, c) = f(a, b)
 */
module.exports = _curry1(function binary(fn) {
  return nAry(2, fn);
});