Martin D Kealey wrote: > On Mon, 16 Feb 2009, Jon Lang wrote: >> if there's any doubt about the matter (e.g., conclusively proving or >> disproving purity would be NP-complete or a halting problem), then > > Deciding whether you have a halting problem IS a halting problem... :-)
You're making the perfect the enemy of the good. I'm not saying that it needs to decide whether or not you have a halting problem; I'm saying that if there's any possibility that you _might_ have one, you should stop looking. Let's take it as a given that things such as exceptions, threads, and co-routines make the automated establishment of whether or not a given function is pure a nightmare. The easy solution for this would be to say that if a given function makes use of exceptions, threads, or co-routines, it will not be auto-tagged as pure. The process of auto-tagging pure functions would not be perfect, in that there are likely to be a number of functions that are in fact pure but don't get auto-tagged as such; but it could still be _good_, in the sense that a useful set of pure functions _would_ be auto-tagged. -- Jonathan "Dataweaver" Lang
