echo foo(2,3) # 23
Is this a sort of comment? Is it documented somewhere?
It's for term-rewriting templates:
https://nim-lang.github.io/Nim/manual_experimental.html#term-rewriting-macros
The section is pretty detailed. In the wild I use in Arraymancer to catch multiply -> add and rewrite them as an optimized fused operation for example: https://github.com/mratsim/Arraymancer/blob/532f45a6/src/tensor/optim_ops_fusion.nim#L53-L74