cond.js•1.57 kB
var _arity = require('./internal/_arity');
var _curry1 = require('./internal/_curry1');
var map = require('./map');
var max = require('./max');
var reduce = require('./reduce');
/**
* Returns a function, `fn`, which encapsulates if/else-if/else logic.
* `R.cond` takes a list of [predicate, transform] pairs. All of the arguments
* to `fn` are applied to each of the predicates in turn until one returns a
* "truthy" value, at which point `fn` returns the result of applying its
* arguments to the corresponding transformer. If none of the predicates
* matches, `fn` returns undefined.
*
* @func
* @memberOf R
* @since v0.6.0
* @category Logic
* @sig [[(*... -> Boolean),(*... -> *)]] -> (*... -> *)
* @param {Array} pairs
* @return {Function}
* @example
*
* var fn = R.cond([
* [R.equals(0), R.always('water freezes at 0°C')],
* [R.equals(100), R.always('water boils at 100°C')],
* [R.T, temp => 'nothing special happens at ' + temp + '°C']
* ]);
* fn(0); //=> 'water freezes at 0°C'
* fn(50); //=> 'nothing special happens at 50°C'
* fn(100); //=> 'water boils at 100°C'
*/
module.exports = _curry1(function cond(pairs) {
var arity = reduce(max,
0,
map(function(pair) { return pair[0].length; }, pairs));
return _arity(arity, function() {
var idx = 0;
while (idx < pairs.length) {
if (pairs[idx][0].apply(this, arguments)) {
return pairs[idx][1].apply(this, arguments);
}
idx += 1;
}
});
});