The keyboard

Four ways to enter a glyph

1. Tap the board. Keyboard shows it. Keys are laid out like the 2741's, so tapping also shows you where the key is. ABC switches to letters and digits.
2. The 2741 layout. Unshifted letters are capitals; Shift-R is ⍴, Shift-L is ⎕. Hold Alt for the character a key is painted with.
3. Overstrikes. Ctrl-] strikes the last glyph, so ⍟ is ○, that key, *. On the board, the row under the keys has each overstrike this mode has, one tap each, with the two it is struck from shown small beneath it; the board's BACKSPACE strikes any pair. On the ABC tab, the A̲ key underscores letters: one tap for the next letter, two quick taps to lock it for every letter, and a tap to let go.
4. Paste. APL pasted in arrives as it is. Several lines run one by one, each as if typed and entered -- a whole function definition, then a call -- and the last, unfinished line stays to be finished. Escape stops them.

The board's special keys

• ← (Backspace, on the picture) is the 2741's overstrike key: it does not erase. The next character strikes over the last one, so ○, ←, * is ⍟. A note under the line says a strike is waiting; ← again or Erase cancels it. A pair that makes nothing rings, and the note says what the first one does make: the lamp ⍝ is ∩ with ○, not with ∘.
• Erase deletes the last glyph, a struck one whole.
• The row under the keys (APL tab) has every overstruck glyph this mode has, one tap each, with its two parts beneath.
• A̲ (ABC tab) underscores letters: one tap for the next letter, two quick taps to lock it, a tap to stop. The note under the line says which.
• Caps Lock switches the picture between APL glyphs and letters, as the APL and ABC tabs do.
• ATTN stops a running line.
• ⬍ moves the board to the other edge; − and + size its keys.

The keyboard

APL80 is typed on the TRS-80's own keyboard, which has no APL characters. An unshifted letter is a capital, for names. A shifted letter is a symbol, and the screen shows it as the letter with a dot at its left: shifted P, ·P, is ⍴, and shifted I, ·I, is ⍳, so ·I3 gives 1 2 3.

• Substitutes: % divides, @ is the logarithm, $ not equal, & and, " the outer product's jot.
• The minus signs: - is the negative sign, -3, and _ subtracts, 5_2. In a name a - is part of it: M-N is one name.
• The arrows: [ \ ] ^ type ↑ ↓ ← →. An up or down arrow with nothing on its left grades.
• Round brackets index a variable: A(2). ·D after a number is the axis: +/1·DM sums the columns.
• ·F sets the numeric format, ·S is status, ·C begins a comment, # turns characters into their codes and back, and ·U peeks and pokes once )RAM is open.

Three ways to type

1. Tap the board. Keyboard shows it: each key is the character to type, with the symbol it stands for under it.
2. Your own keyboard. Letters type capitals; hold Shift for a shifted letter's symbol.
3. Paste. Several lines run one by one, each as if typed and entered -- a whole )DEF definition, then a call -- and the last, unfinished line stays to be finished. Escape stops them.

Defining and changing functions

There is no del. )DEF Z←SQ X opens a new function and asks for line 1; each line typed is the next, and an empty line, for the TRS-80's BREAK, closes it. )EDIT SQ reopens one. While it is open:

• )? shows the whole function, the header as line 0; )P 5 shows 14 lines from line 5.
• )3 deletes line 3 and asks for its replacement; )0 asks for a new header.
• )E 3 puts line 3 in the input line to type over.

A name already in use is a DEFN ERROR: )ERASE it, or open it with )EDIT. )HELP EDITOR has the whole list.

The machine

• )RAM opens the TRS-80's memory: ·U 16384 peeks, 7 ·U 16384 pokes, and 15360 to 16383 is the screen. 51 # 65 prints an A.
• )DOS takes DIR, KILL NAME and RETURN.
• )TRON traces each line of a function as it runs; )PS and )PD print 6 digits or 15; )AUTO sets a line to run when the workspace is loaded, and )EXEC runs it.

Defining and changing functions

∇Z←S W;V opens a new function, and the prompt [1] numbers the line you type next; ∇ closes it. ∇S reopens one. While it is open:

• [3] goes to line 3, [3] text replaces it, [1.5] puts a line between 1 and 2, and [∆3] deletes line 3.
• [⎕] shows the whole function, [3⎕] line 3 alone, and [⎕3] from line 3 on. ∇S[⎕]∇ shows S without leaving the prompt.
• In (B) '75, [3⎕] puts line 3 in the input line to edit in place; press Return to enter it.
• In (A) '70, [3⎕10] changes part of line 3: it is shown, and under it, from column 10, / deletes the character above and a digit opens that many blanks before it. The line is shown again; type into the blanks and press Return.

A function name already in use is a DEFN ERROR: )ERASE it, or reopen it with ∇NAME. )HELP EDITOR has the whole list.