Hi Dario,
I think it would be a great idea to make this unification between letrec
and with. The current implementation of letrec is extremely simple and
almost like syntactic sugar, so there is some work to do, but it should be
feasible of course...
Cheers,
Yann
Le dim. 26 juin 2022 à 13:49, Dario Sanfilippo <sanfilippo.da...@gmail.com>
a écrit :
> Hello, list.
>
> This is a topic that we've briefly discussed in past, and it has come to
> our attention again while working on some refactoring in the libraries with
> Stéphane.
>
> When implementing recursive systems, I often end up using this pattern as
> it allows me to write versatile and readable code:
>
> fun(param0, ..., paramN) = loop ~ si.bus(M)
> with {
> loop(state0, ..., stateM) = y0, ..., yM
> with {
> y0 = state0 * param0;
> ...
> };
> };
>
> Consider this function:
>
> onePoleSwitching(att, rel, x) = loop ~ _
> with {
> loop(yState) = (1.0 - coeff) * x + coeff * yState
> with {
> coeff = ba.if(x > yState, ba.tau2pole(att), ba.tau2pole(rel));
> };
> };
>
> We cannot write this using `letrec` as in this example:
>
> onePoleSwitching(att, rel, x) = y
> letrec {
> 'y = (1.0 - coeff) * x + coeff * y;
> }
> with {
> coeff = ba.if(x > y, ba.tau2pole(att), ba.tau2pole(rel));
> };
>
>
> since `y` is not visible within the `with` scope.
>
> We could write:
>
> onePoleSwitching(att, rel, x) = y
>
> letrec {
> 'coeff = ba.if(x > y, ba.tau2pole(att), ba.tau2pole(rel));
> 'y = (1.0 - coeff) * x + coeff * y;
> };
>
> but this would introduce a delay in the `coeff` signal, which would make
> the filter output not correct.
>
> What I was wondering is, since the first implementation using `with` is
> possible, could we combine `with` and `letrec` for a more concise and
> powerful environment such as the example below or is there anything that
> I'm missing in the syntax that makes it non-computable?
>
> onePoleSwitching(att, rel, x) = y
>
> with {
> 'y = (1.0 - coeff) * x + coeff * y;
> coeff = ba.if(x > y, ba.tau2pole(att), ba.tau2pole(rel));
> };
>
> Ciao,
> Dario
>
> Dr Dario Sanfilippo
> http://dariosanfilippo.com
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