urbit/base/pub/doc/hoon/runes/br/brfs.md
2015-04-29 18:48:45 -04:00

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[barfas, `|/`, %brfs](#brfs)
============================
Door with tile
`|/` is a synthetic rune that produces a [`%gold`]() [door]() with
sample `[%bctr p]` and list of [arm]()s `q`. The list of arms must be
closed with a `--`.
`|/` is similar to `|_` in that it accepts a sample for the set of arms
, but differs in that it accepts [wet or `%ash`]() arms.
See also
--------
[barcab, `|_`, `%brcb`]() [barcen, `|%`, `%brcn`]()
Produces
--------
Twig: `[%brfs p=tile q=(map term foot)]`
Sample
------
`p` is a tile. `q` is a [`map`]() with [`++term`]() keys and
[`++foot`]() values.
Tall form
---------
|/ p
+- p.n.q
q.n.q
--
Wide form
---------
None
Irregular form
--------------
None
Examples
--------
/~zod/try=> =fas |/
a=@
+- two (mul a 2)
+- for (div a 2)
--
new var %fas
/~zod/try=> ~(two fas 2)
4
/~zod/try=> ~(for fas ~(for fas ~(two fas 12)))
6
In this simple example we're creating a door with two arms. One arm
divides our sample by two, the other divides by two.
/~zod/try=> =kom
|_ a=(list)
++ hed -.a
++ tal +.a
--
new var %kom
/~zod/try=> =kot
|/ a=(list)
+- hed -.a
+- tal +.a
--
new var %kot
/~zod/try=> ~(tal kom "abc")
t=~[98 99]
/~zod/try=> ~(tal kot "abc")
t="bc"
/~zod/try=> ~(tal kot [1 2 3 ~])
[2 3 ~]
/~zod/try=> ~(tal kom [1 2 3 ~])
t=~[2 3]
Here we're demonstrating the difference between `|_` and `|/`. We create
a nearly identical door using both runes, each with an arm that produces
the tail of the sample, `a`. You can see that our wet gates use the
sample as a tile to produce well-typed output.
++ by :: map engine
~/ %by
|/ a=(map)
::
+- all
~/ %all
|* b=$+(* ?)
|- ^- ?
?@ a
&
?&((b q.n.a) $(a l.a) $(a r.a))
All of the container engines in `hoon.hoon` use `|/` to set up the tile
for their operations. In `++by`, the map engine, `|/` creates a door
that takes a map that is passed to its arms. See more about using `++by`
in the [library]().