An array is covert if its display is empty, that is, if it has a 0 in the non-trailing elements of its shape.
i. 0 7 NB. covert i. 4 3 0 2 NB. covert i. 2 0 NB. non-covert i. 0 NB. non-covert
It is possible to represent a noun covertly:
f=: i.@(0&,)@(a.&i.)@(3 : '5!:5 <''y''')
g=: ".@({&a.)@(}.@$)
x=: 2 4$ ;:'any noun onomatopoeia eleemosynary synecdoche'
f x
$f x
0 50 32 52 36 60 59 46 95 49 32 39 32 97 110 121 32 110 111 117 110 32 111 110 ...
g f x
┌──────────┬────┬────────────┬────────────┐
│any │noun│onomatopoeia│eleemosynary│
├──────────┼────┼────────────┼────────────┤
│synecdoche│any │noun │onomatopoeia│
└──────────┴────┴────────────┴────────────┘
x -: g f x
1
Contributed by RogerHui. An earlier version of the text previously appeared in the J Forum on 2007-08-02.