urbit/base/pub/doc/hoon/runes/wt/wtdt.md

wutdot, ?., %wtdt

If, else

?.is a synthetic hoon that produces r if p is yes (&, 0), or q if p is no (|, 1). ?. is sort of like "if not", producing the second expression if the loobean is true. ?. is the inverse of ?:.

See also

wutcol, ?:, %wtcl

Produces

Twig: [%wtdt p=twig q=twig r=twig]

Sample

p, q, and r are twigs.

Tall form

?.  p
  q
r

Wide form

?.(p q r)

Irregular form

None

Examples

~zod/try=> ?.((gth 1 2) 1 2)
1
~zod/try=> ?.(?=(%a 'a') %not-a %yup)
%yup

Here we see two common cases of ?. in the wide form, one uses an expression gth that produces a loobean and the other ?= to produce one of its cases.