Dijkstra used this notation for his formal work later on[1]. He didn't like invisible infix operators, so he introduced "." as the function application operator

Dijkstra used this notation for his formal work later on[1]. He didn't like invisible infix operators, so he introduced "." as the function application operator and made it left associative. So f.x.y is the same as (f.x).y. I find it very elegant now that I've gotten over the usual knee jerk aversion to new syntax. [1] https://www.cs.utexas.edu/users/EWD/transcriptions/EWD13xx/EWD1300.html https://www.cs.utexas.edu/users/EWD/transcriptions/EWD13xx/E...