Re: Supporting fractional values for a unit converter function

On Sunday, March 22nd, 2026 at 2:05 AM, Heime <[email protected]> wrote:

> I want to extend a unit conversion framework that accepts fractional
> inches by letting value be a Lisp rational (like 7/64) and then treating
> it as a normal number in the conversion.
> 
> To write (units 7/64 :inch :mm) rather than the cumbersome
> (units ((float 7) / (float 64)) :inch :mm)

Can a function be made to take an argument 7/64 and interpret 
it inside the function as (/ (float 7) (float 64))?
 
> (defun units (value from to)
>   (cond
>     ;; inches to cm
>     ((and (eq from :inch) (eq to :cm))
>        (* value 2.54))
> 
>     ;; cm to inches
>     ((and (eq from :cm) (eq to :inch))
>        (/ value 2.54))
> 
>     ;; catch invalid combinations
>     (t nil)))