Re: [boost] [GSoC] [Boost.Hana] Formal review request

Subject: Re: [boost] [GSoC] [Boost.Hana] Formal review request
From: Larry Evans (cppljevans_at_[hidden])
Date: 2014-07-30 13:29:16

On 07/29/2014 04:54 PM, Louis Dionne wrote:> Larry Evans <cppljevans
<at> suddenlink.net> writes:
>
>>
>> [...]
>>
>> I looked at:
>>
>> http://ldionne.github.io/hana/index.html
>>
>> but saw no mention of the `let-expressions` that was mentioned here:
>>
>> http://article.gmane.org/gmane.comp.lib.boost.devel/245231
>>
>> Did I miss where they are documented or was there some problem
>> in implementing them and, consequently, they were left out?
>
> That was for the MPL11. With Hana, we use generic C++14 lambdas instead,
> so we don't need that emulation anymore.
>
> Regards,
> Louis
>

So, let me check to see if I understand how generic c++14 lambdas
would be used to emulate let-expressions.

The let-expressions I'm talking about are described here:

http://docs.racket-lang.org/reference/let.html

Generic c++14 lambda expression are described here:

https://isocpp.org/wiki/faq/cpp14-language#generic-lambdas

The correspondence between the two, IIUC, is the let-expresion:

  ( let
    ( [id1 val-expr1]
      [id2 val-expr2]
      [id3 val-expr3]
      ...
    )
    body-expr
  )

would be, using generic-lambdas:

  []
  ( auto id1
  , auto id2
  , auto id3
  )
  { return body-expr
  }
  ( val-expr1
  , val-expr2
  , val-expr3
  ...
  )

Is that about right?

TIA.

-regards,
Larry