[GiggleLiu]

Very good question. Floating point `+=` and `-=` are not exactly reversible. This is the only approximation that we have made in NiLang. To compile NiLang to a reversible device (rigorously reversible), we need to overhaul current number systems, i.e. using fixed point numbers and logarithmic numbers instead. Fixed point numbers are exactly reversible under `+=` and `-=`, logarithmic numbers are exactly reversible under `*=` and `/=`. Here is an example of implementing Bessel function with two number systems: https://giggleliu.github.io/NiLang.jl/dev/examples/besselj/