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This reverts commit 8e1e40d75b3ab15c194b6bf9570f3edc46e2de58. This reverts commit f073c490f9fd7c5abc033af4857df92229877de7. This reverts commit f187d2d7e01a54823f3e979af9bbd148b398e7e9. This reverts commit bc272862a73cfce1b118586ca39d3a377d841f1b. This reverts commit 30a397513f8890a3406dc7ab91c6e067e3bbfbbb. This reverts commit 4fc6856fb50d88c20a0f533392ca606641c5f38f. Conflicts: urb/urbit.pill urb/zod/base/lib/drum.hoon
115 lines
2.5 KiB
Markdown
115 lines
2.5 KiB
Markdown
[bardot, `|.`, %brdt](#brdt)
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============================
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Trap
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`|.`, is a synthetic hoon that produces a [dry]() [`%gold`]() trap. A
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trap is a [`door`]() with one only arm [`$`](), the empty name.
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The default action performed on a trap is kicking it by pulling the arm
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`$`. `|.` is similar to `|=` with no arguments. You can think of `|.` as
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a function that takes no inputs.
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See also
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--------
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[barhep, `|-`, %brhp](#brhp) [bartis, `|=`, %brts](#brts)
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Produces
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--------
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Twig: `[%brdt p=twig]`
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Sample
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------
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`p` is a [`++twig`]().
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Tall form
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---------
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|. p
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Wide form
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---------
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|.(p)
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Irregular form
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--------------
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None
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Examples
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--------
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/~zod/try=>
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=a |.(42)
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changed %a
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/~zod/try=>
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a
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< 1.yln
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[ a
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< 2.yqy
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[ a
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< 3.kii
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[ a
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< 2.wvx
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[ a=<2.kqf 2.hng 250.qyy 41.raw 414.hhh 100.xkc 1.ypj %164>
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<2.hng 250.qyy 41.raw 414.hhh 100.xkc 1.ypj %164>
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]
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>
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<2.hng 250.qyy 41.raw 414.hhh 100.xkc 1.ypj %164>
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]
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>
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<2.hng 250.qyy 41.raw 414.hhh 100.xkc 1.ypj %164>
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]
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>
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<2.hng 250.qyy 41.raw 414.hhh 100.xkc 1.ypj %164>
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]
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>
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/~zod/try=>
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(a)
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42
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/~zod/try=>
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$:a
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42
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This is a simple example. We assign a shell variable `a` to be a trap
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that simply produces the atom `42`. Printing `a` prints the core and its
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context. Calling `a` using `(`, the irregular form of [`%-`](), produces
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its value. As does pulling the arm `$` from inside it using `$:a`.
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/~zod/try=>
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=a 10
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changed %a
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/~zod/try=>
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=b |. (add a 2)
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changed %b
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/~zod/try=>
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(b)
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12
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In this case we assign a variable `a` to be `10`, and create a trap `b`
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to add `2` to it. This is a trivial example, but is meant to show that
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traps are useful when you need a gate that only operates on values that
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are already in its context.
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/~zod/try=>
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=loop =+ reps=10
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=+ step=0
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=+ outp=0
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?: =(step reps)
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outp
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$(outp (add outp 2), step +(step))
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changed %loop
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/~zod/try=> (loop)
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20
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Expanding on our previous example, we create a trap with three local
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variables, `reps`, `step`, and `outp`. We use a trap to create a loop,
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testing each time if `step` is equal to `reps`, if so producing `outp`
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otherwise calling our trap again with `outp` replaced with `outp+2`, and
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`step` incremented.
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