Ahhh... FORTRAN -- my first language: CDC 3100, 1965. What magic.
Still have my copy of "FORTRAN 77 For Engineers and Scientists" just in case.
It was very easy to pick up for someone who had only used AppleII or TRS-80 BASIC.
Don't know if it's still the case, but in FORTRAN IV you don't need spaces between keywords and variable names. So when the compiler sees "FORI=2" it has to look still further ahead to decide if this is a for-loop (FORI=2TO9DO) or an assignment to a variable named FORI. Decidedly not a context-free grammar; you can't even figure out the tokens without the ad-hoc parser getting involved.
WAs told in my first week after a hours quick instruction on our 11/40 - to get the book on Fortran from the company library and learn it.