[jerf]

GHC is effectively an attempt to strong-man that argument over a couple of decades, and in short, it failed. It has pretty good performance for what all Haskell is doing, but if you want to write C-speed Haskell you are restricted to a tiny portion of Haskell that you can only understand with deep knowledge of GHC, and based on what I've seen of it, it is completely unrealistic to call it "Haskell" anymore. It's more a language that happens to be embedded inside of Haskell, but unspecified. (Sort of like "the performant subset of Javascript if you want the JIT to do its best"... it exists, but it's undocumented, it isn't the same between engines, and it's very hard to write it without an intense knowledge of the innards.)

The "sufficiently smart compilers" turn out to either not exist, or be beyond the ability of even the smartest humans.

This is not celebration of that, or condemnation that anyone tried. It's a major bummer, actually, and I am suitably bummed. I'd love to have the Sufficiently Smart Compiler. But wanting doesn't count for much. At this point if someone wants to argue that something at a Haskell level of "functional programming" can run at C speed routinely, they need to produce the compiler; we ran the gamut on mere theories.

(I have to qualify it that way because we do have a lot of evidence that you can have "functional flavored" languages that run much more quickly, like O'Caml (at least in single thread) and Rust, if you consider that "functional flavored". But straight-up Haskell does not appear to be able to "just" get transformed to C-speed code reliably.)