Terser function syntax + trailing functions

[DerpMcDerp]

Terser function syntax

:{ foo() }       // :() foo()
:{ foo($, $) }   // :(a) foo(a, a)
:{ foo($0, $2) } // :(a, _, c) foo(a, c)

:{ foo($, $1) } // syntax error, can't mix $ and $<digit>

:{ a }     // => :() -> _ = { return a; }
:{ a; }    // => :() -> _ = { a; }
:{ a; b; } // => :() -> _ = { a; b; }

:{ a; b } // syntax error, only single expressions can have elided semi-colons

Trailing function syntax

foo(1, 2) :(x) = {
	return x + 3;
} :{
	$ + 4
}

foo() :{ x + $ }.c();

// =>

foo(
	1,
	2,
	:(x) = { return x + 3; },
	:{ $ + 4 }
);

foo(:{ x + $ }).c();

So, combining the above allows cpp2 to resemble Swift so you can onboard them onto cpp2:

std::ranges::for_each(a) :{
	std::cout << $;
}

std::ranges::transform(a, b) :{
	$ + 1
}

where_is = std::ranges::find_if(a) :{
	$ == waldo$
}

foo()
:{ a() } // error, ":" must be on the same line as foo()


foo() :(X) x + 3;
// error, can only use lambda forms with braces as the trailing function, e.g.
// foo() :(X) = { return x + 3; }
// or
// foo() :{ $ + 3 }