Re: macro that uses local variables

[Heime <heimeborgia@protonmail.com>]

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------- Original Message -------
On Tuesday, August 8th, 2023 at 1:27 PM, Emanuel Berg <incal@dataswamp.org> wrote:


> Heime wrote:
> 
> > I am using the rocket equation in this macro [...]
> > 
> > (defmacro booster-velocity-change
> > (specific-impulse standard-gravity initial-mass final-mass)
> > "Compute change of velocity using rocket equation."
> > `(* (* ,specific-impulse ,standard-gravity)
> > (log (mass-ratio ,initial-mass ,final-mass))) )
> 
> 
> There is no reason to write a macro for this
> simple computation.
> 
> > I want to change it such that the arguments are set as local
> > variables
> 
> 
> Lexical scope, defun, arguments, if need be `let'. It is
> super easy.
> 
> If you start thinking "how do I solve my problem?" instead of
> "how do I do <something> in Emacs", everything will be much
> easier for you ...

In the context of a macro, the 'let' command should happen outside tho macro
quote.  With the quote expression in the body.  Am I right ?

(defmacro booster-velocity-change
    (specific-impulse initial-mass final-mass)
  "Compute change of velocity using rocket equation."

 (let ( (gravity 9.81) )
   `(* (* ,specific-impulse ,gravity)
      (log (mass-ratio ,initial-mass ,final-mass))) ))
 
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