Not that i'm the proshit haskell expert, but I don't think that GHC does the most amazing job in applying optimizations and I definitely think its performance paradigm is really hard to reason about.
Still, it was a nice breakdown of a real non-toy problem in haskell!
I've heard quite the opposite. I've heard that GHC is state of the art in the depth and breadth of optimizations it can perform. I'm struggling to remember if the context was "of everything" or just within pure functional programming.
GHC has great optimizations within the scope of modules (and seems to balance for the right level of polymorphism/modularity/linking), and can inline some things across module boundaries. But at the level of entire programs more advanced optimizations are possible; I gather there are tradeoffs too.
Still, it was a nice breakdown of a real non-toy problem in haskell!