functional JS

_JS

function _curry(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(a, b); };
  }
}

function _curryr(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(b, a); };
  }
}

var _get = _curryr(function(obj, key) {
  return obj == null ? undefined : obj[key];
});

function _filter(list, predi) {
  var new_list = [];
  _each(list, function(val) {
    if (predi(val)) new_list.push(val);
  });
  return new_list;
}

function _map(list, mapper) {
  var new_list = [];
  _each(list, function(val, key) {
    new_list.push(mapper(val, key));
  });
  return new_list;
}

function _is_object(obj) {
  return typeof obj == 'object' && !!obj;
}

function _keys(obj) {
  return _is_object(obj) ? Object.keys(obj) : [];
}

var _length = _get('length');

function _each(list, iter) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    iter(list[keys[i]], keys[i]);
  }
  return list;
}

var _map = _curryr(_map),
  _each = _curryr(_each),
  _filter = _curryr(_filter);

var _pairs = _map(function (val, key) { return [key, val]; });

var slice = Array.prototype.slice;
function _rest(list, num) {
  return slice.call(list, num || 1);
}

function _reduce(list, iter, memo) {
  if (arguments.length == 2) {
    memo = list[0];
    list = _rest(list);
  }
  _each(list, function(val) {
    memo = iter(memo, val);
  });
  return memo;
}

function _pipe() {
  var fns = arguments;
  return function(arg) {
    return _reduce(fns, function(arg, fn) {
      return fn(arg);
    }, arg);
  }
}

function _go(arg) {
  var fns = _rest(arguments);
  return _pipe.apply(null, fns)(arg);
}

var _values = _map(_identity);

function _identity(val) {
  return val;
}

var _pluck = _curryr(function(data, key) {
  return _map(data, _get(key));
});

function _negate(func) {
  return function(val) {
    return !func(val);
  }
}

var _reject = _curryr(function(data, predi) {
  return _filter(data, _negate(predi));
});

var _compact = _filter(_identity);

var _find = _curryr(function(list, predi) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    var val = list[keys[i]];
    if (predi(val)) return val;
  }
});

var _find_index = _curryr(function(list, predi) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    if (predi(list[keys[i]])) return i;
  }
  return -1;
});

function _some(data, predi) {
  return _find_index(data, predi || _identity) != -1;
}

function _every(data, predi) {
  return _find_index(data, _negate(predi || _identity)) == -1;
}


function _push(obj, key, val) {
  (obj[key] = obj[key] || []).push(val);
  return obj;
}

var _group_by = _curryr(function(data, iter) {
  return _reduce(data, function(grouped, val) {
    return _push(grouped, iter(val), val);
  }, {});
});


var _inc = function(count, key) {
  count[key] ? count[key]++ : count[key] = 1;
  return count;
};

var _count_by = _curryr(function(data, iter) {
  return _reduce(data, function(count, val) {
    return _inc(count, iter(val));
  }, {});
});

var _head = function(list) {
  return list[0];
};

Collections-1: 수집하기 - map

// 컬렉션 중심 프로그래밍의 4가지 유형과 함수
// 1. 수집하기 - map > values, pluck 등
// 2. 거르기 - filter > reject, compact, without 등
// 3. 찾아내기 - find > some, every 등
// 4. 접기 - reduce > min, max, group_by, count_by

###########
function _is_object(obj) {
  return typeof obj == 'object' && !!obj;
}

function _keys(obj) {
  return _is_object(obj) ? Object.keys(obj) : [];
}

function _each(list, iter) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    iter(list[keys[i]], keys[i]);
  }
  return list;
}

function _map(list, mapper) {
  var new_list = [];
  _each(list, function(val, key) {
    new_list.push(mapper(val, key));
  });
  return new_list;
}

function _filter(list, predi) {
  var new_list = [];
  _each(list, function(val) {
    if (predi(val)) new_list.push(val);
  });
  return new_list;
}

function _curry(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(a, b); };
  }
}

function _curryr(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(b, a); };
  }
}

//var _map = _curryr(_map),
//  _each = _curryr(_each),
//  _filter = _curryr(_filter);

var [_map,_each,_filter] = [_curryr(_map),_curryr(_each),_curryr(_filter)];

#############
var users = [
  { id: 10, name: 'ID', age: 36 },
  { id: 20, name: 'BJ', age: 32 },
  { id: 30, name: 'JM', age: 32 },
  { id: 40, name: 'PJ', age: 27 },
  { id: 50, name: 'HA', age: 25 },
  { id: 60, name: 'JE', age: 26 },
  { id: 70, name: 'JI', age: 31 },
  { id: 80, name: 'MP', age: 23 },
  { id: 90, name: 'FP', age: 13 }
];
############

#1-1 values
function _identity(val) {return val;}  
var _values = _map(_identity); 
console.log(_values(users[0]));

#1-2 pluck
var _pluck = _curryr(function(data, key) {
  return _map(data, _get(key));
});
console.log( _pluck(users, 'age') );

Collections-2: 거르기 - filter

// 컬렉션 중심 프로그래밍의 4가지 유형과 함수
// 1. 수집하기 - map > values, pluck 등
// 2. 거르기 - filter > reject, compact, without 등
// 3. 찾아내기 - find > some, every 등
// 4. 접기 - reduce > min, max, group_by, count_by
#####
var users = [
  { id: 10, name: 'ID', age: 36 },
  { id: 20, name: 'BJ', age: 32 },
  { id: 30, name: 'JM', age: 32 },
  { id: 40, name: 'PJ', age: 27 },
  { id: 50, name: 'HA', age: 25 },
  { id: 60, name: 'JE', age: 26 },
  { id: 70, name: 'JI', age: 31 },
  { id: 80, name: 'MP', age: 23 },
  { id: 90, name: 'FP', age: 13 }
];
#####
#2-1 reject
function _negate(func) {
  return function(val) {
    return !func(val);
  }}
  
var _reject = _curryr(function(data, predi) {
  return _filter(data, _negate(predi));
});

#2-2
var _compact = _filter(_identity);

Collections-3: 찾아내기 - find

// 컬렉션 중심 프로그래밍의 4가지 유형과 함수
// 1. 수집하기 - map > values, pluck 등
// 2. 거르기 - filter > reject, compact, without 등
// 3. 찾아내기 - find > some, every 등
// 4. 접기 - reduce > min, max, group_by, count_by

######
var _find = _curryr(function(list, predi) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    var val = list[keys[i]];
    if (predi(val)) return val;
  }
});

var _find_index = _curryr(function(list, predi) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    if (predi(list[keys[i]])) return i;
  }
  return -1;
});

function _some(data, predi) {
  return _find_index(data, predi || _identity) != -1;
}

function _every(data, predi) {
  return _find_index(data, _negate(predi || _identity)) == -1;
}

Collections-4: 접기 - reduce

var users = [
  { id: 10, name: 'ID', age: 36 },
  { id: 20, name: 'BJ', age: 32 },
  { id: 30, name: 'JM', age: 32 },
  { id: 40, name: 'PJ', age: 27 },
  { id: 50, name: 'HA', age: 25 },
  { id: 60, name: 'JE', age: 26 },
  { id: 70, name: 'JI', age: 31 },
  { id: 80, name: 'MP', age: 23 },
  { id: 90, name: 'FP', age: 13 }
];
//var users2 = {
//  36: [{ id: 10, name: 'ID', age: 36 }],
//  32: [{ id: 20, name: 'BJ', age: 32 }, { id: 30, name: 'JM', age: 32 }],
//  27: [],
//  ...
//}

#############
//   1. min, max, min_by, max_by

function _min(data) {
  return _reduce(data, function(a, b) {
    return a < b ? a : b;
  });
}
function _max(data) {
  return _reduce(data, function(a, b) {
    return a > b ? a : b;
  });
}

function _min_by(data, iter) {
  return _reduce(data, function(a, b) {
    return iter(a) < iter(b) ? a : b;
  });
}
function _max_by(data, iter) {
  return _reduce(data, function(a, b) {
    return iter(a) > iter(b) ? a : b;
  });
}
var _min_by = _curryr(_min_by),
  _max_by = _curryr(_max_by);
console.log(
  _min_by([1, 2, 4, 10, 5, -4], Math.abs)
);

console.log(
  _min([1, 2, 4, 10, 5, -4])
);
console.log(
  _max([1, 2, 4, 10, 5, -4])
);
console.log(
  _max_by([1, 2, 4, 10, 5, -4, -11], Math.abs)
);
console.log(
  _min_by(users, function(user) {
    return user.age;
  })
);

_go(users,
  _filter(user => user.age >= 30),
  _map(_get('age')),
  _min,
  console.log);
_go(users,
  _reject(user => user.age >= 30),
  _max_by(_get('age')),
  _get('name'),
  console.log);
  
###############
//   2. group_by, push

function _push(obj, key, val) {
  (obj[key] = obj[key] || []).push(val);
  return obj;
}

var _group_by = _curryr(function(data, iter) {
  return _reduce(data, function(grouped, val) {
    return _push(grouped, iter(val), val);
  }, {});
});

var _head = function(list) {
  return list[0];
};

####
_go(users,
  _group_by(_get('age')),
  console.log);
  
_go(users,
  _group_by(function(user) {
    return user.age - user.age % 10;
  }),
  console.log);
  
_go(users,
  _group_by(function(user) {
    return user.name[0];
  }),
  console.log);
  
_go(users,
  _group_by(_pipe(_get('name'), _head)),
  console.log);

##### 
//   3. count_by, inc

var _inc = function(count, key) {
  count[key] ? count[key]++ : count[key] = 1;
  return count;
};

var _count_by = _curryr(function(data, iter) {
  return _reduce(data, function(count, val) {
    return _inc(count, iter(val));
  }, {});
});
   
console.log(
  _count_by(users, function(user) {
    return user.age - user.age % 10;
  })
);
_go(users,
  _count_by(function(user) {
    return user.name[0];
  }),
  console.log);
console.log( _pairs(users[0]) );

ar f1 = _pipe(
  _count_by(function(user) { return user.age - user.age % 10; }),
  _map((count, key) => `<li>${key}대는 ${count}명 입니다.</li>`),
  list => '<ul>' + list.join('') + '</ul>',
  document.write.bind(document));
_go(users, _reject(user => user.age < 20), f1);
_go(users, _filter(user => user.age < 20), f1);

  

FN- currying & closure

const p3 = (a)=>(b)=>(c)=>a+b+c ;
p3(1)(2)(3);

####

function _curry(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(a, b); };
  }
}
function _curryr(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(b, a); };
  }
}
var _get = _curryr(function(obj, key) {
  return obj == null ? undefined : obj[key];
});

var _length = _get('length');

For each&map&filter... reduce

function _is_object(obj) {
  return typeof obj == 'object' && !!obj;
}

function _keys(obj) {
  return _is_object(obj) ? Object.keys(obj) : [];
}

function _each(list, iter) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    iter(list[keys[i]], keys[i]);
  }
  return list;
}

function _map(list, mapper) {
  var new_list = [];
  _each(list, function(val, key) {
    new_list.push(mapper(val, key));
  });
  return new_list;
}

function _filter(list, predi) {
  var new_list = [];
  _each(list, function(val) {
    if (predi(val)) new_list.push(val);
  });
  return new_list;
}

function _curry(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(a, b); };
  }
}

function _curryr(fn) {
  return function(a, b) {
    return arguments.length == 2 ? fn(a, b) : function(b) { return fn(b, a); };
  }
}

var _map = _curryr(_map),
  _each = _curryr(_each),
  _filter = _curryr(_filter);
  
###

function _reduce(list, iter, memo) {
  if (arguments.length == 2) {
    memo = list[0];
    list = _rest(list);
  }
  _each(list, function(val) {
    memo = iter(memo, val);
  });
  return memo;
}

New-style

let [start, end] = [this.start, this.end];

object_keys

function _is_object(obj) {
  return typeof obj == 'object' && !!obj;
}

function _keys(obj) {
  return _is_object(obj) ? Object.keys(obj) : [];
}

var _length = _get('length');

Pipe & GO

function _is_object(obj) {
  return typeof obj == 'object' && !!obj;
}

function _keys(obj) {
  return _is_object(obj) ? Object.keys(obj) : [];
}

function _each(list, iter) {
  var keys = _keys(list);
  for (var i = 0, len = keys.length; i < len; i++) {
    iter(list[keys[i]], keys[i]);
  }
  return list;
}

var slice = Array.prototype.slice;
function _rest(list, num) {
  return slice.call(list, num || 1);
}

###

function _reduce(list, iter, memo) {
  if (arguments.length == 2) {
    memo = list[0];
    list = _rest(list);
  }
  _each(list, function(val) {
    memo = iter(memo, val);
  });
  return memo;
}

###

function _pipe() {
  var fns = arguments;
  return function(arg) {
    return _reduce(fns, function(arg, fn) {
      return fn(arg);
    }, arg);
  }
}
function _go(arg) {
  var fns = _rest(arguments);
  return _pipe.apply(null, fns)(arg);
}