cmat ← ##.display  array                    ⍝ Boxed display of array.
cmat ← ##.displays array                    ⍝ .. with axis lengths.
cmat ← ##.displayr array                    ⍝ ..    ..  and subarray depths.

The argument array is  displayed  with boxes bordering each subarray. Characters
embedded in the borders indicate subarray shape and type.

Shape:  ↓ → Non-zero axis.
        ⌽ ⊖ Zero axis.

Type:     ∊ Nested array.
          ~ Numeric.
          - Character.
          # Namespace reference.
          ∇ ⎕OR object.
          + Mixed type.

Prototypical items of empty arrays (⌽ ⊖) are exposed.

With  one  exception,  [display] perfectly distinguishes arrays. That is to say,
distinct  arrays  have distinct display forms. The exception, signalled by a '+'
character  in  its  left  lower border, is a depth-1 (sub) array containing both
characters and numbers. For example: display 88,'99'.

Variations
----------
Inspired  by  David  Rabenhorst's  1988  paper, Dick Bowman supplies two further
versions of the display function

    displays    ⍝ display with shape along top border.
    displayr    ⍝ display with shape along axis borders and with depth.

Compare the output from Dick's functions with the original:

        display 1 'a' 'abc' (2 3⍴⍳6)    ⍝ "standard" display.
    ┌→──────────────────┐
    │     ┌→──┐ ┌→────┐ │
    │ 1 a │abc│ ↓1 2 3│ │
    │   - └───┘ │4 5 6│ │
    │           └~────┘ │
    └∊──────────────────┘

        displays 1 'a' 'abc' (2 3⍴⍳6)   ⍝ with shape along top border.
    ┌→─4────────────────┐
    │     ┌→─3┐ ┌→─2 3┐ │
    │ 1 a │abc│ ↓1 2 3│ │
    │   - └───┘ │4 5 6│ │
    │           └~────┘ │
    └∊──────────────────┘

        displayr 1 'a' 'abc' (2 3⍴⍳6)   ⍝ with shape per axis and depth.
    ┌4────────────────────┐
    │     ┌3───┐ ┌3─────┐ │
    │ 1 a │ abc│ 2 1 2 3│ │
    │   - └────┘ │ 4 5 6│ │
    │            └~─────┘ │
    └¯2───────────────────┘

Ref: "The Compact Display of Arbitrary Nested Arrays" D. A. Rabenhorst (IBM),
     APL88 Conference Proceedings, pp 272-277, ACM - 0-89791-253-5/88/0002/0272

Examples:

      display 'ABC'(1 4⍴1 2 3 4)(0 1 0⍴0)(⎕SE #)('88',99)
┌→────────────────────────────────────────┐
│ ┌→──┐ ┌→──────┐ ┌┌⊖┐ ┌→───────┐ ┌→────┐ │
│ │ABC│ ↓1 2 3 4│ ⌽↓0│ │ ⎕SE  # │ │88 99│ │
│ └───┘ └~──────┘ └└~┘ └#───────┘ └+────┘ │
└∊────────────────────────────────────────┘

See also: disp box dsp

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