programming language where you provide an 'initial guess' return value every time you define a function
or maybe you provide a fast way to compute an initial guess from input parameters at runtime, and it can use that in parallel with slower/more accurate ways to get the result, like interlacing an image on a slow connection
so the program is always working but gets more and more accurate over time
or maybe the initial guess is actually the input to some fixpoint-computing procedure that converges on a more accurate value