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Date: Wed, 22 Apr 2020 13:09:13 -0500
To: "php internals" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Function pipe operator
From: larry@garfieldtech.com ("Larry Garfield")

On Wed, Apr 22, 2020, at 3:25 AM, Guilliam Xavier wrote:
> On Tue, Apr 21, 2020 at 4:44 PM Larry Garfield <larry@garfieldtech.com> wrote:
> >
> > On Mon, Apr 20, 2020, at 11:20 PM, Stanislav Malyshev wrote:
> > > Just a small pedantry note - in a comparison section, the RFC compares
> > > this syntax to function composition. But this is not function
> > > composition. This is a syntax sugar for calling two functions one after
> > > another, not operator that produces a function. It sounds pedantic but
> > > it's rather important distinction - if |> is composition, than $foo |>
> > > $bar is a new callable provided $foo and $bar are callable (but no
> > > function is actually being called here!). If |> is call syntax, it's
> > > actually the result of calling $bar($foo).
> > >
> > > So comparing it to function composition is a bit confusing. Otherwise it
> > > looks OK to me, except the syntax for calling functions and methods is a
> > > bit awkward, but it's not the problem of this RFC I imagine.
> >
> > I'm not sure I follow.  The only place composition is mentioned is in the F# section, where it calls out specifically that we're implementing "pipe forward" and *not* the composition operators ( >> ).  Is that unclear?
> 
> Actually it's also mentioned in the Haskell section, but as "function
> concatenation" (which adds to the confusion I guess).

Ah, I see what you mean.  I've adjusted that section to be clearer about what Haskell does.

> Speaking of Haskell, that reminded me of
> http://learnyouahaskell.com/a-fistful-of-monads#walk-the-line where
> the author defines a custom `-:` operator such that `x -: f` desugars
> to `f x` (equivalent to how `$x |> $f` would desugar to `$f($x)` with
> the RFC), which allows to write e.g. `xs -: sort -: reverse` instead
> of `reverse (sort xs)` or `(reverse . sort) xs`.

If I ever actually wrote Haskell, I'd find that extremely useful. :-)

--Larry Garfield