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Introduction

Orchestrating tasks expressed as functions - playing with ideas for the future Gulp task system. The idea here is to experiment with tasks-as-functions idea expressed here: https://github.com/gulpjs/gulp/issues/355#issuecomment-45052782

In a nutshell we would like to have task dependencies expressed as (asynchronous) functions, instead of tasks as of today. It would make it possible to covert today's code:

gulp.task('foo', function(done) {
    //do something foo-lish here
    done();
});

gulp.task('bar', function(done) {
    //do something bar-ish here
    done();
});

gulp.task('default', ['foo', 'bar'], function(done) {
    // do something when 'foo' and 'bar' are done
});

into:

function foo(done) {
    //do something foo-lish here
    done();
}

function bar(done) {
    //do something bar-ish here
    done();
};

gulp.task('default', gulp.parallel(foo, bar) , function(done) {
    // do something when 'foo' and 'bar' are done
});

or, if you prefer to have foo and bar being executed in a sequence:

gulp.task('default', gulp.series(foo, bar) , function(done) {
    // do something when 'foo' and 'bar' are done
});

Obviously one should be able to combine the parallel and series calls, ex.:

gulp.task('default', gulp.series(foo, gulp.parallel(bar, baz) , function(done) {
    // do something when 'foo' and 'bar' and 'baz' are done
});

Such approach has several advantages over the current system:

• it is possible to precisely control order of execution of dependent tasks
• a set of dependent tasks to be executed could be built dynamically
• using function dependencies instead of tasks make it possible to define / expose only tasks that make sense for the users; in a way those functions can act as "private tasks".

Spec

A discussion about a new task system for Gulp4 is scattered over several GitHub repositories and issues. I would love to centralise this discussion and open it up to the community for discussion.

Different ways of specifying dependencies

• gulp.task('default', [], function() {})) - should work as of today
• gulp.task('default', ['foo', 'bar'], function() {})) - where foo and bar are tasks should work as of today
• gulp.task('default', gulp.parallel('foo', 'bar'), function() {})) - where foo and bar are tasks should be equivalent to the above
• gulp.task('default', gulp.parallel(foo, bar), function() {})) - where foo and bar are function references
• gulp.task('default', gulp.series(foo, bar), function() {})) - where foo and bar are function references

Asynchronous functions that can be combined

The gulp.parallel and gulp.series arguments should accept any asynchronous functions. The end-of-processing for a given function can be expressed be:

• synchronously returning a value / throwing an exception
• invoking a provided callback
• returning a promise
• returning a stream
• it would be really easy to extend it to other node-async processing patterns (process, http request etc.)

Implementation

This repo contains a minimal, non-production ready implementation of a promise-based functions dependency system that could potentially replace the current task orchestration system.

There is a separate repository containing a POC for a minimal gulp implementation based on this function orchestration.