Stefan O'Rear wrote:
Unfortunately, ignoring purity is fraught with peril. One notable example recently is in HAppS, a Haskell web framework. Alex Jacobson (a haskeller of significant note, not some "clueless newbie") accidentally wrote { length xs > 0 } instead of { not (null xs) } in some parsing code. Which would just be inefficient, normally, but it demanded the whole thing, which as it happened was a lazy stream coming of a socket. Bad data dependencies, bang, deadlock.
Ouch! That's gotta sting... I wasn't aware that this function was so leathal. I use it constantly all the time...
Option 2. Ignore lists
It's possible to describe lists threaded with something else.
data ListT m a = m (ListT' m a) data ListT' m a = NilT | ConsT a (ListT m a)
You get your safety back ... and lose the standard list functions, list syntax, list comprehensions, list instances, strings-as-lists, et cetera.
That's... interesting... (I feel yet another "I'm going to have to sit down and think about that one" comming on.)