Typing glyphs

APL uses a large range of special graphic symbols to represent most functions and operators. While keyboard mappings become memorized over time, entering APL characters can frustrate the beginner. However, a study involving high school students found that typing and using APL characters did not hinder the students in any measurable way. There are several convenient ways to enter the glyphs.

How to Set up an APL Keyboard

Linux

Geoff Streeter authored a paper, Supporting APL keyboards on Linux, which was presented at the Dyalog '10 user meeting. In this paper, Geoff details how APL keyboards can be supported in X11 using xkb, the X Keyboard Extension.

Most Linux distributions released after mid-2012 have Dyalog keyboard support included with the distribution.

setxkbmap

The simplest way to set up an APL keyboard on Linux is with the following setxkbmap command. Enter the following in your terminal emulator of choice:

setxkbmap -layout us,apl -variant ,dyalog -option grp:switch

An explanation:

• -layout us,apl assigns us (U.S. English) to be the primary layout, whereas apl is secondary
• -option grp:switch assigns Right Alt to switch to the secondary apl layout when it is pressed, otherwise us is used
• -variant ,dyalog assigns the Dyalog APL variant to the apl layout which contains modifiations unique to the Dyalog language (Note the preceding comma)

A full list of keys that can be used to switch layouts is included in /usr/share/X11/xkb/rules/evdev.lst under the option category.

Note: these changes are not permanent; the user will have to select one of a myriad of methods to run the command on startup. Alternatively, if they use one of the desktop environments listed below, they can follow those instructions.

Xfce

A tutorial specific to Xfce's config files can be found at this GitHub repository.

Windows

• Adám Brudzewsky's keyboard layouts for Windows, which uses AltGr.
• The Dyalog Unicode IME uses Ctrl. It is also possible to install the IME alongside a regular Dyalog APL installation:

Approaches to Layout and Input

Most of today's APLs use a mapping which derives from the original APL\360 terminals' keyboard layout. For example, Dyalog APL's standard US English layout for is as follows:

┌────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬─────────┐
│~ ⌺ │! ⌶ │@ ⍫ │# ⍒ │$ ⍋ │% ⌽ │^ ⍉ │& ⊖ │* ⍟ │( ⍱ │) ⍲ │_ ! │+ ⌹ │Backspace│
│` ⋄ │1 ¨ │2 ¯ │3 < │4 ≤ │5 = │6 ≥ │7 > │8 ≠ │9 ∨ │0 ∧ │- × │= ÷ │         │
├────┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬──────┤
│Tab    │Q   │W   │E ⍷ │R   │T ⍨ │Y   │U   │I ⍸ │O ⍥ │P ⍣ │{ ⍞ │} ⍬ │| ⊣   │
│       │q ? │w ⍵ │e ∊ │r ⍴ │t ~ │y ↑ │u ↓ │i ⍳ │o ○ │p * │[ ← │] → │\ ⊢   │
├───────┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴┬───┴──────┤
│Caps    │A   │S   │D   │F   │G   │H   │J ⍤ │K ⌸ │L ⌷ │: ≡ │" ≢ │Enter     │
│Lock    │a ⍺ │s ⌈ │d ⌊ │f _ │g ∇ │h ∆ │j ∘ │k ' │l ⎕ │; ⍎ │' ⍕ │          │
├────────┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──┬─┴──────────┤
│Shift      │Z ⊆ │X   │C   │V   │B   │N   │M   │< ⍪ │> ⍙ │? ⍠ │Shift       │
│           │z ⊂ │x ⊃ │c ∩ │v ∪ │b ⊥ │n ⊤ │m | │, ⍝ │. ⍀ │/ ⌿ │            │
└───────────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────────────┘

Additional charts for other layouts are available.

There are multiple ways to access the glyphs associated with a particular key.

Text editors

Keyboard layout extensions exist for several popular text editors like VS Code, Emacs and Vim. This is in addition to the availability of the below system-wide settings.

Shifting key

It is quite common to use Ctrl or Alt or AltGr (right-side Alt) as an additional shifting key. For example, AltGr+AltGr+4 would give ≤ while AltGr+Shift+4 would give ⍋.

• The Dyalog Unicode IME uses Ctrl

• NARS2000 uses Alt

• APLX uses AltGr with an option to also use Alt

for example, openSUSE 12.2, Ubuntu 12.10 and Fedora 17.

Prefix key

A prefix key is a special key or character which is entered immediately before typing the corresponding key.

• TryAPL and ngn/apl's scripted demo interface support ` as prefix key.

• The Dyalog Unicode IME and the Dyalog RIDE (Remote Integrated Development Environment) uses ` by default, but allows choosing any key as prefix key.

• Adám Brudzewsky's in-browser language bar recognises all the following as prefix keys: `, ½, ², ^, º, §, ù, µ, °.

US keyboard with Dyalog APL glyphs

Android keyboard

• dzaima's Hacker's Keyboard + APL language using long-press to access APL glyphs.

Keyword look-up

• The Dyalog RIDE (Remote Integrated Development Environment) allows hitting the prefix key (` by default, but configurable) twice, followed by the (beginning of the) name of a symbol or a functionality. It then displays a drop-down of choices with arrow keys to indicate choice and the Tab key to insert the symbol. E.g. `,`,d,i,v,Tab↹ inserts ÷.

ASCII symbol combination

• Many APL glyphs can be approximated by overlaying or juxtaposing two ASCII characters. ngn/apl's scripted demo interface and Adám Brudzewsky's in-browser language bar allow such a pair of characters and hitting the Tab key to replace them with the corresponding APL character. For example, <,-,Tab↹ will insert ← and T,o,Tab↹ will insert ⍕.

On-screen language bar

Several APL IDEs allow the display of a toolbar with a button for each APL glyph:

• Dyalog APL, NARS2000, APL2 and ngn/apl's scripted demo interface all have this feature.

Web browsers

• Adám Brudzewsky's in-browser language bar adds this to most web pages on demand.

Hardware APL keyboard

A couple of hardware keyboards are being sold with APL symbols pre-printed onto the key caps:

• Dyalog sells US English, UK English, and Danish keyboards.

• Unicomp sells both entire keyboards and separate key caps for their keyboard range.