Mnemonics

Mnemonics can assist with remembering the meaning of APL glyphs where on they keyboard they are found for typing them. Both of these skills are essential for an effective APL programmer. This article currently provides examples such aide-mémoires, but will be completed in due time.

Pairing glyphs with their meaning

⋄ (Diamond) separates statements. That is, no functions or operators can break through ⋄, just as diamonds are virtually indestructible.

⌺ looks like a ⋄-shaped Stencil laid on a piece of paper, ⎕.

@ applies a function or substitutes elements at specific locations.

⌶ (I-beam) calls system services. APL was originally developed at IBM, so system services were also IBM services. ⌶ is an I-beam and I-beam is pronounced almost identically to IBM.

The Grade glyphs look like supersonic transports.

⍋ and ⍒ give the indices (grades) needed to sort ascending and descending respectively, and look like an ascending and descending supersonic transport, respectively.

⌽, ⊖, and ⍉ reverse or transpose an array over a given axis. The ○ part of the glyphs symbolise the array, while the line component (|, \, or -) indicates the line across which the reversal/transposal is done.

The log glyph looks like a tree log.

⍟ looks like the cross-section of a tree log

⍱ and ⍲ have the Not glyph ~ on top of or overlaid on the Or glyph ∨ and And glyph ∧ respectively.

⌹ is matrix divide with a ⎕ symbolising a matrix and an inscribed ÷ for "divide".

/ and ⌿ are also called "by" which can be remembered as reduce by.

Pairing glyphs/functionality with their keyboard locations

Below is a US English APL keyboard layout (from Dyalog APL), annotated with short mnemonics. Some of the mnemonics are then fully explained.

⋄ begins new APL expressions just like ` button begins the main section of the keyboard.
⌺ is a modified version of ⌺, so it is Shift+⋄.

¨ applies a function to each 1 of the argument elements, so it is on APL+1.
⌶ looks like a Roman numeral 1, so it also lives on the 1.