I used Mark Jones's HUGS (or its predecessor Gofer) in my elective functional programming course from 1993 through 2010. It worked quite nicely in that context. At some point after 2010, I switched to using GHC to make sure I did not depend on unmaintained software and to be compatible with Haskell 2010 and Simon Thompson's textbook. In recent years, I used Haskell extensively in a required course on programming language organization. Likely, HUGS would have made supporting the large number of students in that course a bit easier. Conrad H. Conrad Cunningham Professor Emeritus & Chair Emeritus The University of Mississippi (Ole Miss) Hm, what does "unmaintained" mean? Sure, long time (more than 10 years)
no updates. Nevertheless, there doesn't seem to be a large number of requests for changes or corrections that are left without response. You may say, there are no users, hence no problems. You may also say that the users are simply quietly satisfied.
And there are a few users, as witnessed by Doug's
https://mail.haskell.org/pipermail/hugs-users/2018-July/000902.html
and Anthony's
https://mail.haskell.org/pipermail/hugs-users/2018-July/000900.html
a bit further along in the same thread.
When I started using Haskell in 2003, inspired by my use of Miranda in a course some 10 years before that, haskell.org had a "Implementation" button with Hugs, nhc, and GHC (of course) and perhaps more, Helium, jhc, uhc, lhc come to mind, I am not sure. Even on top of just wishing the Hugs links repaired, that list would also be high on my wish list.
To be sure, I would never recommend any unmaintained program, such that Hugs very clearly labels itself on https://www.haskell.org/hugs (the wording is "no longer in development"), for any "serious" use. Nevertheless, it seems a waste not to maintain these references to valuable material, whether for educational, historical or just entertainment reasons. One valuable development, not particularly recent but worth mentioning, is Andy Gill's hpc, Haskell Program Coverage, that took place initially, as I understand, using nhc with Malcolm Wallace guidance.