I see you'd need to create a new syntax for this, something like "set in1 0.4" (to set x1[0] to 0.4)

I really need this for some applications where I'm using fexpr~ as signal accumulators/counters

Hmm, it occurred to me it would be nice too and also suit this need to set the current output (perhaps that's even more elegant).

I didn't think about how you couldn't set the current output $y[0] but that's kinda obvious, hehe.

So, yeah, maybe a syntax like set in# and out# for #th input/output set in / out for all inputs/outputs (as it is the standard for the other setting messages).

cheers