huh, can you not use the Xkb APL symbols file?

I thought that compose definitions as well as the shifted layout…

Thank-you. Any thoughts on the layout below versus the others listed?

https://www.pckeyboard.com/page/product/USAPLSET

I've got some notes on setting up input on OpenBSD as well. It enables Left Ctrl and Left Alt for APL symbols, but also a Unicode escape hatch with Right Alt and Caps Lock: https://github.com/turtleyacht/ap-el-kb.github.io

Custom encodings, as was standard (or, well, mandatory) before Unicode (1991). Hell, Dyalog APL to this day supports its classic 1-byte-per-char encoding (not even ASCII-compatible! Nor EBCDIC!) in addition to Unicode.

Looks like the APL chars were added in Uncicode 1.1 (1993), two years after 1.0, which is quick enough.

Early on, the selectric typewriter thing had a spherical ball that could rotate to stamp the characters. So when you typed a key the IBM hardware would type a character on a piece of paper exactly like a typewriter and also the IBM computer would keep track of this and when you ran the expression it would calculate the result and print that out as well. You can see videos of this.

I believe it depends on the era and system, but there were various APL codepages (i.e. definitions for the upper 128 characters) for both EBCDIC and ASCII.

https://en.wikipedia.org/wiki/Digital_encoding_of_APL_symbol...

In the very earliest IBM Selectric teletype-based systems, some APL symbols were constructed by entering one character, hitting backspace, and overstriking a second character. For instance, ⍋ is | overstruck on ∆. It's why a lot of APL symbols look like that.

https://aplwiki.com/wiki/Overstrike

I don’t know if I’m remembering this or making it up but I think many of the early symbols were designed to be combining forms by typewriting two characters on top of each other - overstriking.

Including:

    * asterisk (raise to the power) 
    ⍟ asterisk in circle (logarithm)

    ⊖ Circle with horizontal line (rotate)
    ⌿ Slash with h. line (replicate down)
    ⍀ backslash with h. line (scan down)

    | Vertical line (remainder)
    ⌽ circle with vertical pipe (rotate left/right)

    ⍉ Circle with backslash (transpose/diagonal flip)

    ⊥⊤ pair (encode/decode or vice-versa, not sure)
    ⍎⍕ that pair with circle (eval, format)
    ⌶ that pair together (I-beam system functions)

    ⎕⍞⍠⌸ box, with apostrophe, with colon, with equals
    ⋄⌺ diamond, box with diamond
    ÷⌹ divide, box with divide

    and more ≡≢ ∨∧~⍲⍱ ∇⍒ ⍳⍸ ∊⍷ ~¨⍨ ⍣ 

If that’s real I suppose they were encoded as one byte and somewhere in the print system it was expanded into a compound print instruction; I mildly wonder where that happened.