My understanding, from a long retired uncle (after a 40 year career at the National Institues of Health writing nothing but Fortran), is that Claude writes perfectly idiomatic, performant Fortran. Which I suppose is not a surprise given how it was trained, but I still found amusing to hear.
Have the idioms of Fortran changed much over the decades? Because idiomatic C++ today is unrecognizable to how people had to write for VC++ Win32 until well-until the 2010s.
Yes, infamously so. It was fixed-width at one point.
My humbling Claude experience was pointing at a codebase it took me weeks to get to a good 2003 standard, and watch it do the next fifteen years, cleanup, refactoring, feature additions that needed the tech debt solved I never got round to first, in minutes.