F# Pipeline Operator in JavaScript with Babel

Somewhat related, but I wish that more languages provided a reserved convenience variable for accessing the result of the previous function call:<p><a href="https:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;3326826&#x2F;language-history-origin-of-variable-it-in-read-eval-print-loop&#x2F;3342195" rel="nofollow">https:&#x2F;&#x2F;stackoverflow.com&#x2F;questions&#x2F;3326826&#x2F;language-history...</a><p><pre><code> Python and Ruby: _ Shell: $? HyperTalk: it (my first exposure to the concept, even though it was more of a convention) Some Lisps: *, **, ***, ... </code></pre> If we had that, then we could write:<p><pre><code> func1(); func2(_); func3(_); ... </code></pre> Which reminds me of PostScript, which lets you examine and manipulate the program&#x27;s stack directly (the top of the stack is the previous result):<p><a href="http:&#x2F;&#x2F;www.ugrad.math.ubc.ca&#x2F;Flat&#x2F;intro.html" rel="nofollow">http:&#x2F;&#x2F;www.ugrad.math.ubc.ca&#x2F;Flat&#x2F;intro.html</a><p><a href="http:&#x2F;&#x2F;www.ugrad.math.ubc.ca&#x2F;Flat&#x2F;stack.html" rel="nofollow">http:&#x2F;&#x2F;www.ugrad.math.ubc.ca&#x2F;Flat&#x2F;stack.html</a><p>If I were implementing it, I would make the previous result and stack contents read-only so that it&#x27;s conceptually the same as the pipeline operator except that it allows inspecting the intermediate value.

There&#x27;s also ReasonML for those looking to scratch the itch sooner.<p>Also, don&#x27;t be turned off by the sea of comments. Pick one, they are all great. but yes ML language enthusiasts can be a bit overenthusiastic, but I don&#x27;t fault them for that. They are all anxious to spread the gospel of ML. The Reason community on discord is excellent, one of the best I have had the pleasure to be a part of.<p>I didn&#x27;t go with straight OCaml with js_of_ocaml because I wanted a better representation of what I was doing in JS land. There is an excellent write-up about it here: <a href="https:&#x2F;&#x2F;www.javierchavarri.com&#x2F;js_of_ocaml-and-bucklescript&#x2F;" rel="nofollow">https:&#x2F;&#x2F;www.javierchavarri.com&#x2F;js_of_ocaml-and-bucklescript&#x2F;</a>

Why do people credit the pipe operator to F#? OCaml has it too, and F# is based on OCaml. Did the pipe operator get added to F# first? (The OCaml docs say that the pipe operator first appeared in OCaml 4.01 [1], and I can&#x27;t find out when it got added to F#.)<p>[1] <a href="https:&#x2F;&#x2F;caml.inria.fr&#x2F;pub&#x2F;docs&#x2F;manual-ocaml&#x2F;libref&#x2F;Stdlib.html" rel="nofollow">https:&#x2F;&#x2F;caml.inria.fr&#x2F;pub&#x2F;docs&#x2F;manual-ocaml&#x2F;libref&#x2F;Stdlib.ht...</a>

It&#x27;s times like these that make me realize how spoiled I am by ClojureScript...the -&gt; and -&gt;&gt; macros basically give me a pipe operator, and have been in the language from its inception :)<p>I&#x27;m actually glad that this kind of composition is growing in popularity. Back when I did F# for a living, I loved that by using the pipe operator, you could get something more or less akin to a fluent interface, without any direct coupling between the two composed functions, and without any gross intermediate variables. I have nothing against &quot;regular&quot; point-free composition or anything like that, but I do think that these pipe operators are easier to digest for a lot of purposes.

I find JavaScript unusable without this operator. Fortunately Babel supports it well.<p>It makes a great alternative to fiddling with prototypes or wrapper objects when you want to extend something.<p>For example, this is flat-map implemented as a free function:<p><pre><code> const flatMap = f =&gt; { if (!f) { throw new TypeError(&#x27;f must be a function&#x27;); } return xs =&gt; ({ [Symbol.iterator]: function * () { for (const x of xs) { yield * f(x); } } }); }; &#x2F;&#x2F; Usage const xs = [ 1, 2, 3 ] |&gt; flatMap(x =&gt; [ x, -x ]);</code></pre>

For people who want something similar that is also typescript friendly, I wrote a babel macro that entirely gets compiled away during build.<p><a href="https:&#x2F;&#x2F;github.com&#x2F;ts-delight&#x2F;pipe.macro" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;ts-delight&#x2F;pipe.macro</a>

That fetch &#x2F; await example is horrendous. Please don’t.

Anyone else think the async&#x2F;await example looks terrible? Why do the keywords have to be on their own line?

I had created a solution to scratch my itch while waiting for the pipe operator which even got a logo when it got more than a hundred stars, for anyone interested: <a href="https:&#x2F;&#x2F;github.com&#x2F;egeozcan&#x2F;ppipe" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;egeozcan&#x2F;ppipe</a> (needs ts typings though)

This is nice syntax, but since there are two competing proposals and they&#x27;re collectively at stage 1, this isn&#x27;t something anyone should really be using for nontrivial code, since there&#x27;s a good chance either way that you&#x27;ll be writing JavaScript that will never be valid.

I know this proposal has been sitting around forever, but it really can&#x27;t come fast enough imho. I don&#x27;t know how to help show my support for its inclusion, however. Can anyone help elucidate?

F# pipeline operator aka... function composition that has existed in other MLs forever?

I enjoy the utility of this operator in Elixir but I&#x27;m not sure how I feel about including it in JS.<p>My fear is that JS is trying to be all things to all developers- it feels like we just added the `class` keyword for the OO inclined and now we&#x27;re moving towards functional programming? Do we really want to move further away from the idea of idiomatic JS?<p>But who knows, maybe it will open the door to massive productivity and enjoyability gains with the language...

What was the author thinking with that pointless meme image?

if you add multiplication functionality, identity and termination symbols to it, you get something that is closer to a proper category like done in this: <a href="https:&#x2F;&#x2F;github.com&#x2F;kummahiih&#x2F;python-category-equations" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;kummahiih&#x2F;python-category-equations</a><p>f1(?) |&gt; ( f2(?), I ) |&gt; f3(?) == f1(?) |&gt; f2(?) |&gt; f3(?) , f1(?) |&gt; f3(?)<p>it just feels natural that way

Fun fact: the `pipe` function from `rxjs` can be imported on its own where it will work on any value of type T, not just `Observable&lt;T&gt;`.

I wrote something similar for Scheme - <a href="https:&#x2F;&#x2F;cons.io&#x2F;reference&#x2F;sugar.html#chain" rel="nofollow">https:&#x2F;&#x2F;cons.io&#x2F;reference&#x2F;sugar.html#chain</a>. It&#x27;s interesting to see that other people came up with a quite similar solution, providing two modes: pass-directly, pass-by-variable. Does the JS version supports destructuring?

I think it&#x27;s worth nothing that a full Promise handling pipe function can be written like so:<p><pre><code> const pipe = (...args) =&gt; args.reduce(async (acc, fn) =&gt; fn(await acc)); </code></pre> No actual third party libraries required

It&#x27;s nice that you can&#x27;t typo your variables when writing point-free code

For those of you who work with Node, highland.js is another great route for composable programming. It has excellent support for Node streams, which has made it quite handy with Gulp especially!

The 5 codebox does filter map reduce. That makes me wonder, is there any loop fusion going on in JS? Or are there any good libraries for transducers?

What happens when you need to debug and see how the data looks at each stage of the transformation pipeline? Won&#x27;t the debugger show this as a single step if you use the pipeline operator? It does look cleaner and means you don&#x27;t have to spend time coming up with names for the intermediate results though.

Why not use the haskell bind operator? They&#x27;re similar, right?

Thanks, I hate it.