urbit/base/pub/doc/hoon/runes/cn/cnts.md
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[centis, `%=`, %cnts](#cnts)
============================
Evaluate with changes
`%=` is a natural hoon thatevaluates `p` with the changes specified in
`q`. `%=` is used to change a batch of [wing]()s inside a [`++wing`]()
all at once, ensuring that the product is type checked.
See also
--------
`%_`
Produces
--------
Twig: `[%cnts p=wing q=tram]`
Sample
------
`p` is a [++wing](). `q` is a [++tram]().
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
--------------
p(p.i.q q.i.q, p.i.t.q q.i.t.q)
Examples
--------
/~zod/try=> =+ a=[p=5 q=6]
a(p 2)
[p=2 q=6]
In this example we are using the irregular form of `%=` to replace `p`
in `a`.
/~zod/try=> =+ a=[p=1 q=2 r=3 s=4]
a(p 5, q 6, r 7, s 8)
[p=5 q=6 r=7 s=8]
Here we show how you can replace multiple faces at once. We start with a
new `a` and replace all of its values with the irregular form of `%=`.
/~zod/try=> =+ step=0
=+ leng=10
=+ valu=0
|-
?: =(step leng)
valu
$(valu (mul 2 valu), step +(step))
1.024
In this case we create a simple loop, using [`|-`](). To recurse, we use
`%=` with [`$`](), the empty name — our `|-` — replacing our `valu` with
`(mul 2 valu)` and `step` with `+(step)`.