[Haskell-beginners] Just how unsafe is unsafe

Andrew Wagner wagner.andrew at gmail.com
Thu Feb 5 16:11:17 EST 2009

So we all know the age-old rule of thumb, that unsafeXXX is simply evil and
anybody that uses it should be shot (except when it's ok).
I understand that unsafeXXX allows impurity, which defiles our ability to
reason logically about haskell programs like we would like to. My question
is, to what extent is this true?

Suppose we had a module, UnsafeRandoms, which had a function that would
allow you to generate a different random number every time you call it. The
semantics are relatively well-defined, impurity is safely sectioned off in
its own impure module, which is clearly labeled as such. How much damage
does this do?

Can we push the lines elsewhere? Is sectioning unsafeXXX into Unsafe modules
a useful idiom that we can use for other things as well?
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