brettgilio [1] filed a orphan request for fsharp [2]:

This package has been abandoned for awhile. I own the newer fsharp-
stable package and would take ownership of this package to keep it up
to date instead of having two packages with duplicate purposes.

[1] https://aur.archlinux.org/account/brettgilio/
[2] https://aur.archlinux.org/pkgbase/fsharp/