Re: [Haskell-cafe] Ord methods too strict?

On Jan 4, 2019, at 11:47 AM, Sven Panne wrote:

You *will* leak space if you keep an unevaluated argument around for a long time, there is nothing any implementation can really do about it: It can't know for sure if you will eventually throw away that argument or (partially) evaluate it. Sometimes the optimizer (e.g. via strictness analysis) can help, but not in the general case. So making an argument lazier is not a no-brainer, quite the opposite...

Only if it is repeatedly used in ever deeper unevaluated expressions, such as repeatedly incrementing an IORef counter, without ever forcing the value. In the case of a lazy function ignoring its argument, no space is leaked unless that argument is retained elsewhere, and the function was the sole means of forcing the value. Unreferenced unevaluated thunks get GC'd. Space leaks require ever deeper chains of unevaluated thunks. If laziness always leaked Haskell would not work terribly well. I have code that runs for ~9 hours in constant memory allocating and freeing around 13TB of memory over its lifetime. Various functions it calls do some lazy evaluation or other, and while in some cases forcing the values that are sure to get used might reduce GC activity, there's no space leak. -- Viktor.