IO.js

var compose = require('ramda/src/compose');
var toString = require('ramda/src/toString');

var util = require('./internal/util');

module.exports = IO;

function IO(fn) {
  if (!(this instanceof IO)) {
    return new IO(fn);
  }
  this.fn = fn;
}

IO.prototype['@@type'] = 'ramda-fantasy/IO';

// `f` must return an IO
IO.prototype.chain = function(f) {
  var io = this;
  return new IO(function() {
    var next = f(io.fn.apply(io, arguments));
    return next.fn.apply(next, arguments);
  });
};

//chainRec
IO.chainRec = IO.prototype.chainRec = function(f, i) {
  return new IO(function() {
    var state = util.chainRecNext(i);
    while (state.isNext) {
      state = f(util.chainRecNext, util.chainRecDone, state.value).fn();
    }
    return state.value;
  });
};

IO.prototype.map = function(f) {
  var io = this;
  return new IO(compose(f, io.fn));
};

// `this` IO must wrap a function `f` that takes an IO (`thatIo`) as input
// `f` must return an IO
IO.prototype.ap = function(thatIo) {
  return this.chain(function(f) {
    return thatIo.map(f);
  });
};

IO.runIO = function(io) {
  return io.runIO.apply(io, [].slice.call(arguments, 1));
};

IO.prototype.runIO = function() {
  return this.fn.apply(this, arguments);
};

IO.prototype.of = function(x) {
  return new IO(function() { return x; });
};

IO.of = IO.prototype.of;

IO.prototype.toString = function() {
  return 'IO(' + toString(this.fn) + ')';
};