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gistfile1.js

/*
	Copyright(c) 2013 Susisu
	
	for Node.js
*/

var fs = require("fs");

function main()
{
	async(
		mseq(
			async(
				_set("hoge")(readFile(_("hoge.txt"))),
				_set("fuga")(readFile(_("fuga.txt")))
			),
			_if(_do(function(){return this.hoge && this.fuga;}),
				print(_do(function()
					{
						return this.hoge.toString().toUpperCase() + ", "
							+ this.fuga.toString().toUpperCase();
					})
				),
				print(_("failed to open file(s)"))
			)
		),
		mbind(
			_("piyo.txt"),
			readFile(_return()),
			_do(function(arg){return arg.toString();}),
			print(_return())
		)
	).play({});
}

/*
	Action, the unit of process
*/

function Action(func)
{
	this.func = func;
	this.value = undefined;
	this.onComplete = undefined;
}
Object.defineProperty(Action.prototype, "play", {
	value: function(env, arg)
	{
		this.func.call(env, arg);
	}
});
Object.defineProperty(Action.prototype, "complete", {
	value: function()
	{
		if(this.onComplete)
		{
			this.onComplete();
			this.onComplete = null;
		}
	}
});

/*
	do nothing, return void
*/
function _void()
{
	var action = new Action(function(arg)
	{
		action.complete();
	});
	return action;
}

/*
	do something
*/
function _do(func)
{
	var action = new Action(function(arg)
	{
		action.value = func.call(this, arg);
		
		action.complete();
	});
	return action;
}

/*
	assign
*/
function assign(name)
{
	var action = new Action(function(arg)
	{
		this[name] = arg;
		
		action.complete();
	});
	return action;
}

/*
	set variable (syntax sugar of 'assign')
*/
function _set(name)
{
	return function(value)
	{
		return bind(value, assign(name))
	};
}

/*
	get variable
*/
function _get(name)
{
	var action = new Action(function(arg)
	{
		action.value = this[name];
		
		action.complete();
	});
	return action;
}

/*
	convert non-action value to action
*/
function _(value)
{
	var action = new Action(function(arg)
	{
		action.value = value;
		
		action.complete();
	});
	return action;
}

/*
	do nothing
*/
function _return()
{
	var action = new Action(function(arg)
	{
		action.value = arg;
		
		action.complete();
	});
	return action;
}

/*
	a >>= b
*/
function bind(a, b)
{
	var action = new Action(function(arg)
	{
		var env = this;
		a.onComplete = function()
		{
			b.onComplete = function()
			{
				action.value = b.value;
				
				action.complete();
			};
			b.play(env, a.value);
		};
		a.play(env, arg);
	});
	return action;
}

/*
	a >> b
*/
function seq(a, b)
{
	var action = new Action(function(arg)
	{
		var env = this;
		a.onComplete = function()
		{
			b.onComplete = function()
			{
				action.value = b.value;
				
				action.complete();
			};
			b.play(env);
		};
		a.play(env, arg);
	});
	return action;
}

/*
	(((a >>= b) >>= c) >>= ...)
*/
function mbind()
{
	if(arguments.length > 0)
	{
		var t = arguments[0];
		for(var i = 1; i < arguments.length; i++)
		{
			t = bind(t, arguments[i])
		}
		return t;
	}
	else
	{
		return _void();
	}
}

/*
	(((a >> b) >> c) >> ...)
*/
function mseq()
{
	if(arguments.length > 0)
	{
		var t = arguments[0];
		for(var i = 1; i < arguments.length; i++)
		{
			t = seq(t, arguments[i])
		}
		return t;
	}
	else
	{
		return _void();
	}
}

/*
	do the actions asynchronously
*/

function async()
{
	if(arguments.length > 0)
	{
		var actions = arguments;
		var action = new Action(function(arg)
		{
			var n = 0;
			function handler()
			{
				n++;
				if(n == actions.length)
				{
					action.complete();
				}
			}
			for(var i = 0; i < actions.length; i++)
			{
				actions[i].onComplete = handler;
				actions[i].play(this, arg);
			}
		});
		return action;
	}
	else
	{
		return _void();
	}
}

/*
	if condition then a else b
*/
function _if(condition, a, b)
{
	var action = new Action(function(arg)
	{
		var env = this;
		condition.onComplete = function()
		{
			if(condition.value)
			{
				a.onComplete = function()
				{
					action.value = a.value;
					
					action.complete();
				}
				a.play(env);
			}
			else
			{
				b.onComplete = function()
				{
					action.value = b.value;
					
					action.complete();
				}
				b.play(env);
			}
		};
		condition.play(env);
	});
	return action;
}

/*
	read and return a file content
*/
function readFile(path, stopOnError)
{
	var action = new Action(function(arg)
	{
		fs.readFile(arg, function(err, file)
		{
			if(err && stopOnError)
			{
				console.log(err);
			}
			action.value = file;
				
			action.complete();
		});
	});
	return bind(path, action);
}

/*
	output to console.log
*/
function print(content)
{
	var action = new Action(function(arg)
	{
		console.log(arg);
		
		action.complete();
	});
	return bind(content, action);
}

/*
	call the main function
*/
main();