urbit/base/pub/doc/hoon/runes/cn/cncb.md

cencab, %_, %cncb

Evaluate with changes, cast

%_ is a synthetic rune that evaluates p with the changes specified in q, then casts the product back to the type of p. %_ is used to change a batch of ++wings all at once, ensuring that the resulting product is type checked.

See also

%= is similar, but without type-checking.

Produces

Twig: [%cncb p=wing q=tram]

Sample

p is a ++wing, a list of ++limbs. q is a ++tram, a list of ++wings and twigs.

Tall form

%_  p
  p.i.q  q.i.q
  p.i.t.q  q.i.t.q
==

Wide form

%_(p p.i.q q.i.q, p.i.t.q q.i.t.q)

Irregular form

None

Examples

/~zod/try=> =a [b=1 c=2 d=3]
new var %a
/~zod/try=> %_(a b (add 3 b.a), c (add 3 c.a), d (add 3 d.a))
[b=4 c=5 d=6]

Here we're using %_ to add 3 to all of the values inside of our shell variable a.

/~zod/try=> =a [b='odors' c='twigs' d='tiles']
changed %a
/~zod/try=> %_(a b c.a, c d.a, d b.a)
[b='twigs' c='tiles' d='odors']

In this case we're using %_ to swap the values of the faces in a.

/~zod/try=> =+  a=1    
=+  z=|=(b=@ (add a b))
(z 1)
2
/~zod/try=> =+  a=1    
=+  z=|=(b=@ (add a b))
(%_(z a 100) 1)
101

At first we set up a simple gate z with a variable, a in its context. Subsequently we use %_ to change the value of a within the context of z and compute the output again.