urbit/base/pub/doc/hoon/runes/br/brkt.md
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[barket, `|^`, %brkt](#brkt)
============================
Kicked book
`|^` is a synthetic rune that produces and then kicks a [`%gold`]()
[book]() with sample `p` as a [`%$(p)`](), and a list of [arm]()s `q`.
The list must be closed with a `--`.
`|^` is similar to `|-`, but differs in that it can contain internal
arms.
See also
--------
[barhep, `|-`, %brhp](#brhp) [barcab, `|_`, %brcb](#brcb)
Produces
--------
Twig: `[%brkt p=twig q=(map term foot)]`
Sample
------
`p` is a [twig](). `q` is a [`map`]() with [`++term`]() keys and
[`++foot`]() values, which are called arms.
Tall form
---------
|^ p
++ p.n.q
q.n.q
--
Wide form
---------
None
Irregular form
--------------
None
Examples
--------
/~zod/try=> =+ a=21
|^ [square double]
++ square (mul a a)
++ double (mul 2 a)
--
[441 42]
Here `|^` computes a result by calling its helper arms `++square` and
`++double`. Notice that `a` is also in the context. `|^` is most
commonly used inside another gate or core.
++ mum :: mug with murmur3
~/ %mum
|= a=*
|^ (trim ?@(a a (mix $(a -.a) (mix 0x7fff.ffff $(a +.a)))))
++ spec :: standard murmur3
|= [syd=@ key=@]
?> (lte (met 5 syd) 1)
=+ ^= row
|= [a=@ b=@]
(con (end 5 1 (lsh 0 a b)) (rsh 0 (sub 32 a) b))
=+ mow=|=([a=@ b=@] (end 5 1 (mul a b)))
=+ len=(met 5 key)
=- =. goc (mix goc len)
=. goc (mix goc (rsh 4 1 goc))
=. goc (mow goc 0x85eb.ca6b)
=. goc (mix goc (rsh 0 13 goc))
=. goc (mow goc 0xc2b2.ae35)
(mix goc (rsh 4 1 goc))
^= goc
=+ [inx=0 goc=syd]
|- ^- @
?: =(inx len) goc
=+ kop=(cut 5 [inx 1] key)
=. kop (mow kop 0xcc9e.2d51)
=. kop (row 15 kop)
=. kop (mow kop 0x1b87.3593)
=. goc (mix kop goc)
=. goc (row 13 goc)
=. goc (end 5 1 (add 0xe654.6b64 (mul 5 goc)))
$(inx +(inx))
::
++ trim :: 31-bit nonzero
|= key=@
=+ syd=0xcafe.babe
|- ^- @
=+ haz=(spec syd key)
=+ ham=(mix (rsh 0 31 haz) (end 0 31 haz))
?.(=(0 ham) ham $(syd +(syd)))
--
::
[`++mum`]() is a hashing gate, which uses two helper arms to computes
its results. The `|^` at the top performs the computation.