Function definition mode (typing ∇ followed by a symbol name) is an artifact of the kind of terminal hardware supported by APL (the IBM 2741 with its iconic typeballs) in the 1960s. As such, nearly 50 years later, it may be worth rethinking some of these things to take advantage of newer editor and windowing technologies in common use.
In my opinion, in a windowed environment, function definition mode can be safely disabled provided the system can provide an alternative editor for functions and possibly variables. In SS Windows, Dyalog APL invokes an editor when you double click with the cursor positioned over a name. APL2000 invokes a full screen editor when you type ∇ followed by a name. Function definition mode seems to be retained in some implementations simply to be part of a faithful replica of APL\360. Removing function definition mode would have the side effect of freeing the ∇ character for other uses.
