Promise Generators #752
Description
Hello.
I have updated LiveScript in a fork to support promise generators. The syntax looks like this:
wait = (time) -> new Promise (fulfill) -> setTimeout fulfill, time
my-promise = ->**
console.log \helloWorld
yield wait 1000
console.log \goodbyeWorld
function my-promise **()
console.log \helloWorld
yield wait 1000
console.log \goodbyeWorld
The compiled code renders as such:
// Generated by LiveScript 1.4.0
(function(){
var wait, myPromise;
wait = function(time){
return new Promise(function(fulfill){
return setTimeout(fulfill, time);
});
};
myPromise = generatorToPromise$(function*(){
console.log('helloWorld');
(yield wait(1000));
return console.log('goodbyeWorld');
});
function tryCatch$(func,context,args){
try {
return {
failed: false,
value: func.apply(context,args)
};
}
catch(exception){
return {
failed: true,
value: exception
}
}
}
function generatorToPromise$(func,argumentLength){
function processGenerator(generator){
return new Promise(
function(fulfill,reject){
function next(passIn,handler){
handler = handler || 'next';
var tryCatchResult = tryCatch$(generator[handler],generator,[passIn]);
if(tryCatchResult.failed === true){
return reject(tryCatchResult.value);
}
var result = tryCatchResult.value;
if(result.done){
return fulfill(result.value);
}
else if(result.value instanceof Promise){
result.value.then(
next,
function(promiseError){
next(promiseError,'throw');
}
);
}
else {
next(result.value);
}
}
next()
}
);
}
if(typeof func != 'function' && typeof func.next == 'function'){
return processGenerator(func)
}
else {
if(typeof argumentLength == 'number'){
var args = [];
for(var i = 0; i < argumentLength; i++){
args.push('arg'+i);
}
args = args.join(',');
return new Function('processGenerator,func','return function(' + args + '){ return processGenerator(func.call(this,' + args + ')); };')(processGenerator,func);
}
else {
return function(){
return processGenerator(func.apply(this,arguments));
}
}
}
}
}).call(this);
My only big concern is using this along with currying. The issue is that currying requires knowing the arguments length of the function, but since all functions are being wrapped, the argument length would be zero. To work around this, I have opted to pass in the argument length if the function is curried and create a function via a string. It's pretty gross, but I can't immediately think of a better way that works across platforms.
You can check the fork out here: https://github.com/kkirby/LiveScript/tree/generator-promise
If promise generators are desired, but modifications are requested, I'm open for discussion. Otherwise, is this something that could become a part of LiveScript?