Wikipedia on naming conventions in programming states (without source):
In APL dialects, the delta (Δ) is used between words, e.g. PERFΔSQUARE (…)
This is an unusual choice, but I notice that ECMA-17 says:
(…) in certain applications there is a need for a graphical representation of the control characters which are normally non-printing characters.
Code position Character Pictorial
2/0 SPACE △ SP 7/15 DELETE ▨ DT
Both the standard and the first modern APL implementation became available in '68, but the standard described existing usage, and it would make sense to use an existing substitute character for internal "spaces" in names, since space and juxtaposition has syntactic significance in APL.
Is there any indication that APL's usage of
∆ for separating words in identifiers originates in common usage as a control picture for space? Alternatively, is there any indication of another origin of APL's unusual choice?
⎴) or upticks (
⎵)? (huh, the unicode "TOP SQUARE BRACKET" (shown first) is at the "top" of the character box, there's apparently no similar character to the "BOTTOM SQUARE BRACKET" at the bottom but with the ticks going down ...) (I've always used the one at the bottom with the ticks going up, and I'm finding this question interesting because though I used the delta as a "word separator" in APL identifiers I never knew it had a more general meaning.)