Speaking of compilers in Fortran, Wim Vanderbauwhede has built a compiler for a functional programming language called Funktal:
The compiler is about 5000 lines of Fortran 90: wimvanderbauwhede/funktal: A small compiler implemented in Fortran for a statically typed functional language running on Uxn. - Codeberg.org
I happen to have an uncomplete version of uxn in Fortran: ivan-pi/uxnfort: Uxn virtual machine, written in Fortran, WIP - Codeberg.org; only very rudimentary IO is available and the virtual machine doesn’t yet pass all the opcode tests.