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

[Joost Kremers <joostkremers@fastmail.fm>]

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.


-- 
Joost Kremers
Life has its moments