Anaphoric macros like when-let

Anaphoric macros like when-let

[Arun Isaac]

Is there a Scheme or Guile equivalent to Emacs Lisp's `when-let' ?

Basically, I'm looking for a shorthand to express this:

(let ((x (foo))
  (when x
    (bar x))))

as this:

(when-let (x (foo))
  (bar x))

Re: Anaphoric macros like when-let

[Matt Wette]

> On Aug 26, 2017, at 12:47 PM, Arun Isaac <arunisaac@systemreboot.net> wrote:
> 
> 
> Is there a Scheme or Guile equivalent to Emacs Lisp's `when-let' ?
> 
> Basically, I'm looking for a shorthand to express this:
> 
> (let ((x (foo))
>  (when x
>    (bar x))))
> 
> as this:
> 
> (when-let (x (foo))
>  (bar x))
> 

(use-modules (srfi srfi-2))

(and-let* ((x foo))
  (bar x))

Re: Anaphoric macros like when-let

[Matt Wette]

> On Aug 26, 2017, at 12:50 PM, Matt Wette <matt.wette@gmail.com> wrote:
> 
> 
>> On Aug 26, 2017, at 12:47 PM, Arun Isaac <arunisaac@systemreboot.net> wrote:
>> 
>> 
>> Is there a Scheme or Guile equivalent to Emacs Lisp's `when-let' ?
>> 
>> Basically, I'm looking for a shorthand to express this:
>> 
>> (let ((x (foo))
>> (when x
>>   (bar x))))
>> 
>> as this:
>> 
>> (when-let (x (foo))
>> (bar x))
>> 
> 
> (use-modules (srfi srfi-2))
> 
> (and-let* ((x foo))
>  (bar x))

(and-let* ((x (foo)))
  (bar x))

Re: Anaphoric macros like when-let

[Kyle Siehl]

On Sun, Aug 27, 2017 at 01:17:13AM +0530, Arun Isaac wrote:
> 
> Is there a Scheme or Guile equivalent to Emacs Lisp's `when-let' ?
> 
> Basically, I'm looking for a shorthand to express this:
> 
> (let ((x (foo))
>   (when x
>     (bar x))))
> 
> as this:
> 
> (when-let (x (foo))
>   (bar x))

(cond
 ((foo) => bar))

Or, in general:

(cond
 ((foo)
  => (lambda (x)
       (bar x))))

Re: Anaphoric macros like when-let

[Arun Isaac]

Thank you, Kyle and Matt!

Re: Anaphoric macros like when-let

[Mark H Weaver]

Arun Isaac <arunisaac@systemreboot.net> writes:
> Is there a Scheme or Guile equivalent to Emacs Lisp's `when-let' ?

I have nothing to add to Matt and Kyle's answers, except to mention that
'when-let' is not actually an anaphoric macro.  Anaphoric macros are
those that introduce a binding that is not named by the user, e.g. 'it',
which is called an anaphor.  For more, see:

  https://en.wikipedia.org/wiki/Anaphoric_macro

      Mark

Re: Anaphoric macros like when-let

[Arun Isaac]

Mark H Weaver writes:

> mention that 'when-let' is not actually an anaphoric macro.  Anaphoric
> macros are those that introduce a binding that is not named by the
> user, e.g. 'it', which is called an anaphor.

Yes, you're right, of course! aif, awhen, etc. are the anaphoric
macros. I switched to if-let, when-let, etc. when they became available
in emacs lisp, and somehow wrongly continued to call them anaphoric
macros.