Fortran
Very recently, Los Alamos National Lab published a report An evaluation of risks associated with relying on Fortran for mission critical codes for the next 15 years [1]. In their summary, they write:
Our assessment for seven distinct risks associated with continued use of Fortran are that in the next fifteen years:1. It is very likely that we will be unable to staff Fortran projects with top-rate computer scientists and computer engineers.2. There is an even chance that we will be unable to staff Fortran projects with top-rate computational scientists and physicists.3. There is an even chance continued maintenance of Fortran codes will lead to expensive human or financial maintenance costs.4. It is very unlikely that codes that rely on Fortran will have poor performance on future CPU technologies.5. It is likely that codes that rely on Fortran will have poor performance for GPU technologies.6. It is very likely that Fortran will preclude effective use of important advances in computing technology.7. There is an even chance that Fortran will inhibit introduction of new features or physics that can be introduced with other languages.
In my view, a language is destined for being a "maintenance language" if all of these are simultaneously true:1. There is a dearth of people who know the language well.2. Few people are opting to learn it in their free time, and/or seek it out for a job.3. Companies do not seriously invest in training in learning the language.4. Companies don't pay enough to convince an engineer to use it. who otherwise loves using other languages and has better prospects with them.I've experienced unique challenges in hiring Lisp programmers, but the fact it remains sufficiently interesting to enough software engineers (who are usually good programmers) has been a boon, and likewise providing space to learn it helps even more.Fortran though is teetering on its historical significance and prevalence in HPC. Aside from the plethora of existing and typically inscrutable scientific code, I'm not sure what the big iron imperative language offers over the dozens of other superficially similar choices these days, except beaten-path HPC integration. Scientists are more and more writing their code in C++ and Python—definitively more complicated than Fortran but still regarded as premier languages for superlative efficiency and flexibility respectively. Julia has had a few moments, but (anecdotally) it doesn't seem to have taken off with a quorum of hardcore scientist-programmers.[1] https://permalink.lanl.gov/object/tr?what=info:lanl-repo/lar...