fair enough that maybe i'm not in the target audience. and perhaps i'm too stuck in my own head, writing iOS apps, where i can't imagine general constraint solvers being used to solve a software-design problem (as opposed to an algorithmic problem, where it certainly does make sense). i am genuinely curious - are general constraint solvers useful as a software-design pattern?

are one-way dataflow constraints really any different from the observer pattern? i avoid cycles exactly because i implement it myself, and don't even have a solver, per se. even KVO seems not to handle cycles. and when e.g. i am using auto-layout in IB, even then i am careful to avoid over-constrainedness, even though the solver can settle on a "solution."