What are the secrets to high performance Haskell? I've met people who claim that Haskell code should perform around 5-10x slower than C, Tikhon Jelvis says that mildly optimized Haskell can perform around 3x C in time, kuribas claims that Haskell should perform at least at 50% of C, an acquaintance can get Haskell to half of Rust's performance, and there's libraries like Attoparsec and Streamly that claim 80-90% of C performance. And of course, there's Don Stewart.

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What's the secret to getting high performance Haskell? Are the ultra-fast libraries concurrency scams (i.e, C is single-threaded, Haskell is parallel)? Or are the ultra-fast libraries actually as fast as they claim, and that it's possible to get Haskell to near-C speeds?

Because I love Haskell as a fun toying-around language, given how concise the language (and functional style) can be. Especially when you have defections to the Rust camp, keeping Haskell performant is a worthy goal, and I guess high-performance Haskell is joked about as "only if you're Don Stewart" or "dark magic, summoned by sacrificing puppies and kittens".

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Any tips, links, advice to get ultra-high-performance Haskell, other than, perhaps, inline-C? ;)