Manuel Giraud <[email protected]> writes:
> Heime <[email protected]> writes:
>
>> 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))?
>
> For this a user have to write (/ 7.0 64) as input. See 3rd paragraph of
> the info node "(elisp) Float Basics".
Also, unlike many other Lisps, Emacs Lisp does not provide
rational numbers.
See (info "(elisp) Numbers")
"GNU Emacs supports two numeric data types: “integers” and
“floating-point numbers”. Integers are whole numbers
such as −3, 0, 7, 13, and 511. Floating-point numbers
are numbers with fractional parts, such as −4.5, 0.0, and
2.71828."
In Emacs Lisp, an expression that looks like a rational
number, such as 7/64, will be interpreted as the name of a
symbol, which will either be unbound (likely) or will
reference a variable. Try:
(let ((7/16 "My unexpected variable’s value."))
(message "%s" 7/16))
;;=> "My unexpected variable’s value."
7/16
;;=> Debugger: (void-variable 7/16)
--
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- Geoffrey Chaucer, The Parliament of Birds.
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