Re: Understanding the "let" construct and the setting of variables

[steve-humphreys@gmx.com]

> Sent: Thursday, December 17, 2020 at 2:05 AM
> From: "Joost Kremers" <joostkremers@fastmail.fm>
> To: steve-humphreys@gmx.com
> Cc: help-gnu-emacs@gnu.org
> Subject: Re: Understanding the "let" construct and the setting of variables
>
>
> On Thu, Dec 17 2020, steve-humphreys@gmx.com wrote:
> > For example, the following fails. Why? Haw can one fix the function?
> >
> >  (defun lett (tim tsk)
> >
> >    (let* ( (thr (/ tim 100))
> >            (tmn (- tim (* thr 100)))
> >
> >            (tinc_mn (+ tmn tsk))
> >            (tinc_hr (/ (+ tmn tsk) 60))
> >            (tinc_mn (- tinc_mn (* tinc_hr 60)))
> >
> >            (thr_futur (* (+ thr tinc_hr) 100))
> >            (tmn_futur tinc_mn)
> >            (tim_out (+ thr_futur tmn_futur))
> >
> >            (message "%d %d" tim_out) )
> >
> >       (message "%s" "lett") ))
> >
> > (lett 845 80)
>
> The error is a bit cryptic, but it's telling you that you need to move the first
> `message` into the body of the `let*`. Right now, it's in the list of variables
> to bind, but it's not a valid binding form:
>
> ```
> (defun lett (tim tsk)
>
>   (let* ((thr (/ tim 100))
>          (tmn (- tim (* thr 100)))
>
>          (tinc_mn (+ tmn tsk))
>          (tinc_hr (/ (+ tmn tsk) 60))
>          (tinc_mn (- tinc_mn (* tinc_hr 60)))
>
>          (thr_futur (* (+ thr tinc_hr) 100))
>          (tmn_futur tinc_mn)
>          (tim_out (+ thr_futur tmn_futur)))
>
>     (message "%d %d" tim_out)
>
>     (message "%s" "lett") ))
> ```
>
> Note that this will still produce an error, because the first `message` has a
> format string that requires two arguments but only one is given.

This means that I can use the variables in the body of the "let".  Great explanation,
I fixed to.  Now I need to have the function output "tim_out".

> --
> Joost Kremers
> Life has its moments
>