Re: Executing part of the code instead of another

[<tomas@tuxteam.de>]

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On Wed, Oct 07, 2020 at 03:48:51PM +0200, Christopher Dimech wrote:
> It would be better if you explain to me this progn stuff
> 
> Have tried an example like this
> 
> (setq na 8)
> (setq nb 13)
> ( if (> nb na)
>     progn (
>       (message "nb > na condition [condition is true]")
>       (message "nb > na condition [condition is true]")
>     )

No. Written in Lisp, it's

  (progn
    (thing 1)
    (thing 2)
    ...)

In C (and in conventional maths, you'd write it as you did
above).

Note that it's the same way as you write (message "foo")
[you don't write message("foo"), as you'd do in C or
Python or what not).

Progn is a form to bundle a sequence of forms, which are
evaluated one after the other. The value of progn is
that of the last form evaluated (that's the -n), as opposed
to prog1, which would do the same as progn, but return the
value of its first form.

Cheers
 - t

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