hello! i worked there for 2 years. yes it is a fork called Mu, no it is not not lazy. The Mu Core team are devout Haskellers so don't be too quick to dismiss them as abandoning Haskell's core values.
Thanks for the clarification! I never thought they were not devout Haskellers, but I do always wonder about projects that fork a more standard thing for internal use ending up as poorly maintained legacy software.
They didn't fork GHC. They wrote a new Haskell compiler to target a pre-existing runtime that existed inside the bank. For various reasons related to the runtime that meant the language had to be strict. Mu's creation was, in fact, a step away from legacy.
There is plenty of GHC Haskell in the codebase. It's very common for banks to have proprietary in-house scripting languages. Mu, is at least based on a language standard and is not some ad-hoc design.
The codebases of Facebook and Google would be no less "ancient legacy enterprise monolith".
> It's very common for banks to have proprietary in-house scripting languages
Yeah I don't really understand this. From what I've heard, Goldman Sachs for example, have systems written in a language that no one outside of GS has used, was kinda clever in the early 90s, but hasn't really evolved since and therefore is difficult to get expertise in, and that developers working with it struggle with moving to other companies as their skills are somewhat less transferable.
Edit: at least Facebook and Google open source their internal languages/tools (Go, React, etc) so that those skills become somewhat more transferable.
That might have the same appeal for some, but as much as I like Haskell, that sounds like an ancient legacy enterprise monolith to me.