Re: Fwd: [Patch] definitions in when, unless, do as well as in cond- and case-clauses

["Linus Björnstam" <linus.bjornstam@veryfast.biz>]

You need to use ,optimize. 

-- 
  Linus Björnstam

On Sun, 6 Feb 2022, at 10:27, tomas@tuxteam.de wrote:
> On Sun, Feb 06, 2022 at 07:44:31AM +0100, Linus Björnstam wrote:
>> 
>> On Sat, 5 Feb 2022, at 18:31, Stefan Israelsson Tampe wrote:
>> > Hmm this was wrong, I mean
>> >
>> > For conditional variables we have a default begin. So then why on earth 
>> > do you not have an implicit let?, Just laziness?
>> > There should  be a good reason or? this is a pretty fundamental change 
>> > that I support but then we should not be lazy not trying to understand 
>> > the design choices of the old beards.
>> 
>> In other languages let starts a new lexical context which can be expensive. I don't know guile internals but a let without any defines is trivially converted to a begin by the optimizer.
>
> It seems that in Guile 3 the expander is smart enough for an empty
> bindings list in let:
>
> | tomas@trotzki:~$ guile
> | GNU Guile 3.0.7.6-22120
> | Copyright (C) 1995-2021 Free Software Foundation, Inc.
>
> [...]
>
> | scheme@(guile-user)> ,expand (let () (message #t "Yikes"))
> | $1 = (message #t "Yikes")
> | scheme@(guile-user)> ,expand (let ((x 3)) (message #t "Yikes ~S" x))
> | $2 = (let ((x 3)) (message #t "Yikes ~S" x))
>
> ...but doesn't "see" whether bindings are actually used (quite possibly
> those go away in a later optimisation phase, though):
>
> | scheme@(guile-user)> ,expand (let ((x 3)) (message #t "Yikes"))
> | $3 = (let ((x 3)) (message #t "Yikes"))
>
> Cheers
> -- 
> t
>
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