[jdiez17]

But that's an optimisation. Which can be switched off to get the benefits from parallelism. This is a tradeoff that programmers would traditionally have to consider, but with functional programming the compiler can figure it out for us.

[chongli]

That's assuming that "figuring it out for us" is decidable. Many of the things we wish the compiler could do for us are not.

[dllthomas]

"It's not decidable" is not a guarantee that humans can do better than a compiler. It means any approach will sometimes be wrong, but a compiler might well (in principle) be wrong less often than a human.

This is separate from the "a human has a lot of additional context that's hard to express" argument, which is valid but has nothing to do with decidability.