urbit/pub/docs/dev/hoon/runes/dt/dtwt.md

dotwut,.?, %dtwt

Noun or cell

.?, dotwut, [%dtwt p=twig] is a natural rune that applies nock 3 to a noun: if the noun is a cell, it returns the loobean & (true); if the noun is an atom, it returns the loobean | (false).

Produces

Twig: [%dtwt p=twig]

Sample

p is a twig.

Tall form

.?  p

Wide form

.?(p)

Irregular form

None

Examples

~zod/try=> .?(~)
%.n
~zod/try=> .?(5)
%.n
~zod/try=> .?(~porlep)
%.n

In all of these cases our sample is implicitly down-cast to an atom, which produces |.

~zod/try=> .?([1 2 3])
%.y
~zod/try=> .?("ha")
%.y
~zod/try=> ._a_b__
[%a %b]
~zod/try=> .?(._a_b__)
%.y

[1 2 3] is clearly a cell, "ha" is equivalent to the null-terminated tuple of its ASCII codes, and ._a_b__ is also clearly a cell. Each produce &.