Owl rewrites the standard integer binary operations

[qaristote]

Let's say I open a repl and execute the following code.

#require "owl" ;;
open Owl.Dense.Matrix.D ;;
let n = 5 in get_slice [ [] ; [ 1 ; n - 1 ] ] (eye n) ;;

Then I will get a typing error on n-1 :

Error: This expression has type int but an expression was expected of type
         ('a, 'b) Owl_dense_matrix_generic.t =
           ('a, 'b, Bigarray.c_layout) Bigarray.Genarray.t

The reason is that Owl.Dense.Matrix.D redefines the - operator to work with matrices.

Although this is expected behavior, I wonder whether this is the right choice for the library. As the example shows even when doing linear algebra the integer binary operators may still be used. Of course I could simply use Stdlib.(-) n 1 or define an other symbol for integer operations but I would not call that a great user experience.

I must say it seems like something quite obvious so I wonder if I missed something in the documentation or even whether that's a deliberate choice.

[nilsbecker]

Maybe the idiomatic usage that was intended is

module M = Owl.Dense.Matrix.D
let n = 5;;
let slice = M.get_slice [ []; n-1 ] (M.eye n);;
let zero = M.(eye n - eye n)

?

It might be more ergonomic if Owl used decorated binary operators like -# or some such. I don't know if this has been discussed? In any case it seems a pretty breaking change at this point.

[mseri]

I am not aware of a discussion around this, but I understand the pain. Fwiw, I stumbled upon the same at the beginning and ended up doing what you do in your last comment (and sometime also rely on Stdlib. to recover integer operators).

[nilsbecker]

in view of https://ocaml.xyz/book/convention.html#pure-vs.-impure a more consistent set of operators for element wise algebra might be +. etc. these would overwrite plain float operations. not sure if that's better.