Thorn
Monadic Format means

Format

NB: In the following examples space characters
    are represented by small dots: ···

      4 5 6          ⍝ numeric vector
4 5 6
      ⍕ 4 5 6        ⍝ equivalent character vector
4·5·6
      
      mat            ⍝ numeric matrix
1 2 3
4 5 6

      ⍕ mat          ⍝ equivalent character matrix
1·2·3
4·5·6

N.B. depends on ⎕PP

Dyadic Format means

Format By Specification

Field-width and number of decimal places:

      6 2 ⍕ 3.125 0.002
··3.13··0.00

      6 2 ⍕ mat
··1.00··2.00··3.00
··4.00··5.00··6.00

      6 2 ⍕ 1234   ⍝ (field not wide enough)
******

Language Elements