I share the author's frustration with the lack of non-compiler-related examples of GADT uses. It seems like such a powerful idea, but I haven't been able to get a feel for when to reach for GADTs in Haskell
For example, something like (not an actual example from my code, just conceptually - may be misremembering details):
data Instruction stages where
MovLit :: Word64 -> Register -> Instruction '[Fetch, Decode, Execute, Writeback]
-- MovReg instruction gets rewritten to MovLit in Execute stage
MovReg :: Register -> Register -> Instruction '[Fetch, Decode, Execute]
...
writeback :: (Writeback `member` stages) => Instruction stages -> WritebackState -> WritebackState
writeback (MovLit v reg) = ...
-- Compiler knows (MovReg _ _) is not required here
What you're doing here is pretty cool, I think I will start doing so, too. I have a number of places where I use "undefined" instead. (The "undefined" from the Clash Prelude, which translates into a "don't care" signal state.)
I semi-recently used it for this ADAT fiber optic audio codec https://github.com/YagerICS/adat-codec
Remember if OCaml wasn't a mature programming language, maybe Rust would not have happened in first place.
But being outside of the mainstream may mean you need to occasionally debug more esoteric stuff: https://gallium.inria.fr/blog/intel-skylake-bug/ I'm sure Jane Street can afford doing that, but I'm not so sure if a small team can.
Because despite them being very open about it, no one else does it, and every distinguished engineer who pushes a weird tech choice will justify and defend it.
However, I very much disagree with Graham's 2004 assertion[0]:
It's a lot of work to learn a new programming language. And
people don't learn Python because it will get them a job;
they learn it because they genuinely like to program and
aren't satisfied with the languages they already know.
I was a professional software engineer in 2004, when the Graham post was written. To say, "people don't learn Python because it will get them a job ..." was bullshit then just as it is now. The remainder of the quoted sentence is unfounded extrapolation and has the value of same.
> Yaron Minsky joined Jane Street back in 2002, and claims the dubious honor of having convinced the firm to start using OCaml.
That's pretty cool. And I guess Stephen Dolan ended up there due to his work on OCaml, which is pretty cool too. (I'd like to meet Stephen some day.)
rbjorklin•5mo ago
ackfoobar•5mo ago
Hard to say exactly how much performance one would get, as that depends on access patterns.
misja111•5mo ago
Of course it depends on your use case, in some cases a compact byte array performs better anyway, for instance because now you're able to fit it in your CPU cache.
john-h-k•5mo ago
ackfoobar•5mo ago
Are you saying each byte takes up a word? That is the case in the `char array` in OCaml, but not Java's `byte[]`. AFAIK The size of a byte array is rounded up to words. Byte arrays of length 1-8 all have the same size in a 64-bit machine, then length 7-16 take up one more word.
https://shipilev.net/jvm/objects-inside-out/