I'm using Makoto's 9.0_current builds.
$ doas pkgin install ghc-8.8.1nb2
Password:
calculating dependencies...done.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/xhtml-3000.2.2.1/../integer-gmp-1.0.2.0/
libHSinteger-gmp-1.0.2.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/xhtml-3000.2.2.1/../ghc-prim-0.5.3/
libHSghc-prim-0.5.3-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/xhtml-3000.2.2.1/../base-4.13.0.0/
libHSbase-4.13.0.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/unix-2.7.2.2/../time-1.9.3/
libHStime-1.9.3-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/unix-2.7.2.2/../integer-gmp-1.0.2.0/
libHSinteger-gmp-1.0.2.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
...
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/Cabal-3.0.0.0/../containers-0.6.2.1/
libHScontainers-0.6.2.1-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/Cabal-3.0.0.0/../bytestring-0.10.9.0/
libHSbytestring-0.10.9.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/Cabal-3.0.0.0/../binary-0.8.7.0/
libHSbinary-0.8.7.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/Cabal-3.0.0.0/../base-4.13.0.0/
libHSbase-4.13.0.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
/tmp/lang/ghc88/work/.destdir/usr/pkg/lib/ghc-8.8.1/Cabal-3.0.0.0/../array-0.5.4.0/
libHSarray-0.5.4.0-ghc8.8.1.so, needed by ghc-8.8.1nb2 is not present in this system.
0 to refresh, 0 to upgrade, 0 to install
140M to download, 1893M to install
the following packages have unmet requirements: ghc-8.8.1nb2
proceed ? [Y/n] n