[Haskell-cafe] How to ensure optimization for large immutable vectors to be shared w.r.t. Referential Transparency

[Henning Thielemann]

On Tue, 6 Apr 2021, YueCompl via Haskell-Cafe wrote:

> In an attempt to determine whether two immutable vectors can be treated 
> as the same one to enable specific optimizations for that case, I tried 
> to use ST to determine their respective backing foreign ptrs for 
> comparison. But appears it can be copied when wrapped in a newtype, I 
> wonder why it is the case, and how to avoid the copy?

You compare the ForeignPtrs of the mutable vectors. What about comparing 
the ForeignPtrs of the original immutable vectors?