On Jan 9, 2008 4:21 PM, Don Stewart
anton:
OTOH, the freedom to change things on the fly can be nice to have, and if used with "great responsibility" (mainly an understanding of what's safe to do and what isn't), the downside can be vanishingly small.
It can be small, unless you need to have any kind of static assurance (say for high assurance software, or for new kinds of optimisations, or if you want to reorder code in the compiler for parallelism).
Then the downside to arbitrary, untracked effects in the system is huge.
I just want to point out that unsafePerformIO is at the core of the (safe) bytestring library. As SPJ et al pointed out, this is crucial functionality, and is only unsafe if unsafely used. (Yes, it's unsafe, but you can write a safe module with a purely safe interface that uses unsafePerformIO in its core.) David