[epolanski]

The only non irrelevant compiler ever written in Haskell is for another borderline dead project: Elm.

[gylterud]

What are you on about?

The Agda compiler, Pugs, Cryptol, Idris, Copilot (not that copilot you are thinking of), GHC, PureScript, Elm…

These might not be mainstream, but are (or were for Pugs, but the others are current) important within their niche.