Hello from APL! (And also Haskell, to a smaller extent.)
I bet all these languages come from people with a thick CS theory background, and thus a tradition and a need to write formulae on a blackboard.
Unlike a keyboard, a blackboard is a graphical device, it's slow to produce long character strings, but basically any one glyph takes about the same time to write, be it an x, ≡, ∉, ⊕, ℵ, etc.
Then you want to plainly represent the same concepts in the computer language, et voilà.
I bet all these languages come from people with a thick CS theory background, and thus a tradition and a need to write formulae on a blackboard.
Unlike a keyboard, a blackboard is a graphical device, it's slow to produce long character strings, but basically any one glyph takes about the same time to write, be it an x, ≡, ∉, ⊕, ℵ, etc.
Then you want to plainly represent the same concepts in the computer language, et voilà.