Re: [Emacs-diffs] master 4612b2a 1/2: Implement and-let*

Re: [Emacs-diffs] master 4612b2a 1/2: Implement and-let*

[Stefan Monnier]

>     (internal--build-binding-value-form): Extend to account for
>     solitary symbols and (EXPR) items in binding varlist.

We're forced to accept those forms in `let` and `let*` for historical
reasons, but why do we want to also accept them in newer constructs?


        Stefan

Re: [Emacs-diffs] master 4612b2a 1/2: Implement and-let*

[Mark Oteiza]

On 12/09/17 at 01:21pm, Stefan Monnier wrote:
> >     (internal--build-binding-value-form): Extend to account for
> >     solitary symbols and (EXPR) items in binding varlist.
> 
> We're forced to accept those forms in `let` and `let*` for historical
> reasons, but why do we want to also accept them in newer constructs?

Solitary symbols are expanded as x -> (x (and PREV x)), so it's not the
historical behavior.  (EXPR) means EXPR is an s-expression, which
doesn't make sense in let or let*, e.g.:

   (let (x)
     (and-let* (((null x))) "it's null"))

Re: [Emacs-diffs] master 4612b2a 1/2: Implement and-let*

[Richard Stallman]

[[[ To any NSA and FBI agents reading my email: please consider    ]]]
[[[ whether defending the US Constitution against all enemies,     ]]]
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  > >     (internal--build-binding-value-form): Extend to account for
  > >     solitary symbols and (EXPR) items in binding varlist.

  > We're forced to accept those forms in `let` and `let*` for historical
  > reasons,

It is not just a matter of history.
Those are very convenient in 'let'.
It would be a bad idea not to have them.

Whether they are useful in other new constructs, I don't know.
What do these new constructs look like?

-- 
Dr Richard Stallman
President, Free Software Foundation (gnu.org, fsf.org)
Internet Hall-of-Famer (internethalloffame.org)
Skype: No way! See stallman.org/skype.html.

Re: [Emacs-diffs] master 4612b2a 1/2: Implement and-let*

[Michael Heerdegen]

Richard Stallman <rms@gnu.org> writes:

>   > >     (internal--build-binding-value-form): Extend to account for
>   > >     solitary symbols and (EXPR) items in binding varlist.
>
>   > We're forced to accept those forms in `let` and `let*` for historical
>   > reasons,
>
> It is not just a matter of history.
> Those are very convenient in 'let'.
> It would be a bad idea not to have them.

> Whether they are useful in other new constructs, I don't know.
> What do these new constructs look like?

Just search for SRFI 2, e.g.

  https://www.gnu.org/software/guile/manual/html_node/SRFI_002d2.html

`if-let*' and `when-let*' in Emacs are analogue.

I don't know much about Lisp's history, but I think there was a
misunderstanding about what these special binding forms mean.  For
example, making a binding form consisting of a single symbol mean "bind
the symbol to nil" would not make sense in these new constructs -
instead, we test the symbol's value for nilness.


Michael.