[swift-evolution] Lambda function syntax

[Craig Cruden]

It has probably been 6 months since I have had time to do anything interesting (JDK6 + Oracle SQL recently for contracts recently) so if I am messing up terminology or syntax - please excuse me.  I messed a few things up and had to open up an old Scala project to remind me what I was doing.


The standard map syntax for Scala is:

	a.map(x => x + 5)

or using a placeholder (very limited shorthand - cannot use a placeholder twice for the same value):

	a.map(_ + 5)

if it is a tuple then

	a.map(x => f(x._1, x._2))

or you can pass in a function block (with pattern matching case)

	a.map { case (x, y) => (y, x) }

there might be some mathematical reason behind the “in” keyword - but it is lost on me as well (it has been a good 30 years since University) and gets lost on me.  If I had more time I might get use to it.

I hope I did not mess up those examples as bad.


 

> On 2015-12-23, at 9:52:46, Andrey Tarantsov <andrey at tarantsov.com> wrote:
> 
>> foo.map( bar => bar.boz) // single line
> 
> Well how important is it to use () instead of {} here?
> 
> If you make it
> 
> foo.map { bar => bar.boz }
> 
> then it's like it is now, but with "in" replace by "=>".
> 
>> foo.map { (x, y) => x * 5 + y }
> 
> I actually like the bare version:
> 
> foo.map { x, y => x * 5 + y }
> 
> but not in your example (here it looks atrocious). Take this real code, though:
> 
> 
>         constrain(topBlock, tableView, view) { top, tbl, sup in
>             top.left  == sup.left + horizPadding
>             top.right == sup.right - horizPadding
>             top.top   == sup.top  + topPadding
> 
>             tbl.top    == top.bottom + 16
>             tbl.bottom == sup.bottom
> 
>             tbl.left  == sup.left + horizPadding - horizTableHang
>             tbl.right == sup.right - horizPadding + horizTableHang
>         }
> 
> I think the lack of parens is beneficial in reducing the visual noise here.
> 
>> And yes, I certainly would prefer `=>` rather than `in`.
> 
> It seems like the community can actually agree on this.
> 
> Does anyone know if it has any parsing problems / grammar implications right now? 
> 
>> I think a big problem with `in` is that it’s textual, and doesn’t provide a clear visual separation from keywords/names at the start of the body or the end of the type specifier.
> 
> Yes, agreed. “Not delimited enough”.
> 
>> (Are the [parentheses] around `bar` in your example required? I’m ambivalent to them.)
> 
> No, they are not, as shown above.
> 
>> To be clear, I’m still not a fan of the Ruby syntax. I think it makes the parsing easier for a compiler but harder for a human…
> 
> Depends on the human. To this specific human, the Ruby-style one is the easiest to parse (and mind you, I had very limited experience with Ruby compared to other languages, so it's not just being used to it, but rather an honest love and preference).
> 
> A.
> 

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