Floating point on uLisp?



I was wondering if floating point would ever come to ulisp.
It would be a great enhancement.

Regards ,



Thank you for the suggestion.

I think it would be relatively straightforward to add floating point to the 32-bit versions of uLisp, for the Arduino Due, Zero, and MKRZero, because the Lisp cells are large enough to hold a 32-bit floating-point value.

What sort of applications do you have in mind that require floating point?



I have for instance a magnetometer sensor , to act as a compas.
It needs to calculate the arctan
of 2 coordinates being x en y

Kind regards ,




Can this be done in lisp itself , or does it require extra code in the arduino software ?

Regards ,



@manes6969 :

Dear Ronny,

From what it looks like to me … you aren’t trying to do a neural network, are you? ;) Because that just looks like a typical activation function…

Is it “doable in Lisp itself”? Let’s say: “kind of”. In theory: totally. In practice: it will take an eternity to perform. So unless @johnsondavies has time for that, you will not have “real” floating point.

However: allow me to propose an alternative: How about a good look-up-table (perhaps a classic plist or alist) and extrapolation?

And then, you could simply treat “floats” as “large integers”. That is, e.g. 1.234 can be expressed as 1234. Your table might have a value for 1.2 and a value for 1.3 (that is, a value for 1200 and a value for 1300). You call up these two values, determine their difference, multiply their difference with 34, divide their difference by 100, and - there you go. You could even just “threshold it”, and say, just take the value for 1.2 (or 1200, here). You may make your table more fine-grained around 0, then, and more coarse towards the ends. As to the “ends” … a slight advice: give a minimal and a maximum value which are NOT the asymptotes, so this way you do not end up with weird division-by-zero errors later on.


Hi Aeneas

No I’m not doing a neural network , no knowledge of that.
Let’s hope Johnsondavies has some time to implement it.
There are lot of sensors , like my magnetometer how require floating point.
I also find it a great enhancement for uLisp or whatever embedded language
Like Forth for example.

Anyways your approach to interpolation gives me some thinking about the matter.
Maybe a lookuptable for arctan could be a in between solution

Thanks for the idea :-) !



I hacked single floats into the language in an afternoon a few weeks ago. It’s tedious, but doable: https://github.com/sjl/ulisp-sam-samd/commit/414a504a524c2160434b7e50daa02d0f17256133


Hi sjl

Thanks alot , but how to implement it ?
Just adding the code , in the end , to the ulisp.ino ?


Hi Sjl

I found the code on github.
Great !!

What I notice however is the accuracy.
Let say (* 2.5 2.5) gives 6.24999 instead of 6.25
Is there a way to round the result ??
But apart from that nice piece of code.

Kind regards


The actual numbers aren’t inaccurate (well, not any more than single floats are by their very nature), it’s my printing routine (pfloat) that’s causing what you see.

There are ways to print floating point numbers nicely and accurately, like this: https://lists.nongnu.org/archive/html/gcl-devel/2012-10/pdfkieTlklRzN.pdf but I didn’t have the time to implement that when I was writing that chunk of code.


Hi Sjl

What you wrote isn’t just a chunk of code IMHO.
I don’t have the knowledge to write something like that
I’m an Electronics engineer whit some knowledge of software.
I know assembler , some C code , forth , and a little lisp , because lisp is very close to forth.
You did a great job.
If you could finish this code with more accuracy , then maybe davies could implement it in future versions ??

Kind regards ,


PS: meanwhile I’m gonna use your floating routines for more calculations
like sin , cos , …


The latest release of the ARM version of uLisp now includes floating-point support; see:

Floating-point features