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Date: Sat, 15 May 2021 09:20:48 +0100
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Subject: Re: [PHP-DEV] [RFC] Partial function application
From: rowan.collins@gmail.com (Rowan Tommins)

On 15 May 2021 00:09:41 BST, Paul Crovella <paul=2Ecrovella@gmail=2Ecom> wr=
ote:
>I think this highlights where the misunderstanding of this feature is=2E


I think the fact that there is so much confusion highlights why it is wort=
h considering different designs=2E


>Partial application is about binding arguments=2E ? isn't an argument,
>it's an argument placeholder=2E It does two things: signals to create a
>closure wrapping the function rather than calling it immediately, and
>holds a position in the argument list so that an argument further to
>the right can be fixed (bound) at that time=2E


This is not a correct description of the current syntax=2E Currently, "?" =
represents a *required* argument in the argument list, but *only* if there =
is a fixed value to its right=2E If it appears at the end of the argument l=
ist, or with only other ? tokens to its right, it *only* signals that a par=
tial should be created, and doesn't create a required argument, even though=
 it looks the same=2E

foo(?, 42) creates a closure with one required argument; foo(42, ?) create=
s a closure with no required arguments



>Requiring additional trailing argument placeholders or adding an
>additional token `=2E=2E=2E?` unnecessarily complicates things, burdens t=
he
>user, and only serves to further promote misunderstanding=2E


On the contrary, saying that "?" always means exactly one argument massive=
ly simplifies the description of the feature=2E Why persist with a version =
of the syntax that is so easy to misunderstand when we have a really simple=
 fix available?

I acknowledge the need for a syntax to say "accept zero or more further ar=
guments", but this doesn't need to overload the syntax for "create a requir=
ed argument here"=2E

If the suggestion of =2E=2E=2E? is too long, we could look at other option=
s like =2E=2E=2E or ?? The syntax for "just make a closure and pass all arg=
uments through" would then be "foo(=2E=2E=2E)" or "foo(??)"=2E

There is a *separate* question of whether arguments that weren't *required=
* are passed along anyway=2E I'm less sure there's a right answer there, an=
d would be happy with a version where foo(?, 42) and foo(?, 42, =2E=2E=2E) =
were equivalent - that is, the trailing "all other arguments" token would o=
nly be needed if there wasn't already a placeholder=2E

Regards,

--=20
Rowan Tommins
[IMSoP]