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Comment by abi | Hacker News Reader

With regards to generating random numbers, the Foreign Function Interface is also really useful. Here's a one-line wrapper around random(3).

  foreign import ccall "stdlib.h random" c_rand :: CDouble -> CLong

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That will most likely bite you since you're giving a pure type to a non-referentially transparent function. There is a reason why random functions are in a state monad or IO.

In particular, while you don't really care what order the compiler makes the underlying calls to the C function, you do care that it actually makes all the calls rather than CSEing them away. As a pure function, the compiler has every right to optimize away multiple calls to your FFI-bound random function, in favor of a single call and multiple references to the value.

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