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Comment by bberrry | Hacker News Reader

What's the degree of backward compatibility with FORTRAN releases? I imagine most FORTRAN codebases as being huge and old, so it makes me wonder how many can adopt the latest versions.

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Each new standard usually removes a very small number of features, but Fortran 2018 is mostly a superset of Fortran 77. Most compilers retain absolute backward compatibility, so they can compile a superset of Fortran 66 to 2018, and often some custom language extensions on top.

Only some of the real ancient pre FORTRAN IV stuff has been removed.

I’ve compiled fortran code from approx 1965. Works the same today. I don’t know of anything that is as compatible as standard Fortran code. That being said, quite a few vendor extensions are floating around, and often old codebases rely on a few of these.

You can start with an awesome-fortran list: https://github.com/rabbiabram/awesome-fortran

In my experience nearly all standard old code will still compile just fine, except code which relied on compiler-specific extensions and directives. Unfortunately, there does tend to be a lot of code out there using these proprietary directives.

Things like metacommands [0] will need to be converted to something standard (or removed) to work with modern compilers.

[0] http://www.ousob.com/ng/fortran/ng4e22.php

This will be of help as well:

https://github.com/CodethinkLabs/fortrantools/blob/master/RE...

Most of the patches are upstreamed, but their gcc repo contains the patched versions on top of the latest gcc releases.

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