There is no safe analog of unsafeFreeze

[anonymous]

Summary is quite exhaustive here. Such function is required when one needs snapshot of mutable vector which will be mutated afterwards. Improper usage of unsafeFreeze already caused bug in mwc-random.

Here is safeFreeze I used:

-- Safe version of unsafeFreeze.
safeFreeze :: (PrimMonad m, Vector v a) => G.Mutable v (PrimState m) a -> m (v a)
safeFreeze v = do
  v' <- GM.unsafeNew (GM.length v)
  GM.unsafeCopy v' v
  unsafeFreeze v'

[rl]

Happily, the current darcs version already has this:

-- | /O(n)/ Yield an immutable copy of the mutable vector.
freeze :: (PrimMonad m, Vector v a) => Mutable v (PrimState m) a -> m (v a)
{-# INLINE freeze #-}
freeze mv = unsafeFreeze =<< M.clone mv