Re: ?-suffix for booleans... good-idea? or bad-idea?

[Panicz Maciej Godek]

2017-04-27 12:39 GMT+02:00 Jan Nieuwenhuizen <address@hidden>:

> Christopher Allan Webber writes:
>
> > I've noticed that it's common in Guile modules to use "foo?" for
> > variable names involving booleans.  It's tempting,
>
> > But is it a good idea?
>
> It's an idea that I like and use.  Not sure that says anything about
> good or bad.
>
> I would like to help you paint though!
>
> We have functions like null? and pair? that return booleans, where I
> would like the [non]-nil value.  I often find myself writing things like
>
>    (let ((bar (if (pair? foo) (baz foo)
>                #f)))
>
> where I would rather like to write something like
>
>    (let ((bar (and=> (pair?=> foo) baz)))
>
> How do you do these things, and how do you call your pair?=> function?
>
>
I usually use the and-let* form (SRFI-2) to deal with  such cases.

(and-let* (((pair? foo)))
  (baz foo))

The (grand scheme) library which I maintain provides a variant of and-let*
that additionally provides pattern matching:

https://github.com/plande/grand-scheme/blob/master/grand/syntax.scm#L255

so you could even write the above code as

(and-let* (((_ . _) foo))
  (baz foo))