Martin,

What is the best way to install Hat for both ghc and nhc98?

I would recommend unpacking the source tarfile twice, and building each version in a separate tree. (In theory it should be possible to build in the same tree, but at the moment there are clashes between .hi files from ghc and nhc98.)

However, it seems that the hat binaries are built differently when building for ghc and nhc98.

Which set of binaries should I choose?

The stand-alone programs (hat-trans, hat-observe, hat-trail, etc) are built by either ghc or nhc98, which is why they differ. For hat-trans, the ghc-built version runs faster than the nhc98-built version, but the nhc98-built version uses less heapspace. For the browsing tools, I don't think it really matters which version you choose - they run at about the same speed when built by either ghc or nhc98. (However, I have noticed that using ^C to interrupt a list of equations in hat-observe only seems to work in the nhc98-built version.) Obviously, the compiler-specific `hat' packages (containing libHShat.a, and some .hi files) must both be installed. Regards, Malcolm