From cce2b5c9ed3a0b1625e95d9216e272ab44485de0 Mon Sep 17 00:00:00 2001
From: Edward Amsden <edward@blackriversoft.com>
Date: Tue, 16 May 2023 18:09:09 -0500
Subject: [PATCH] hoon: add pin and awl arms to test and trim subaxes

---
 pkg/arvo/sys/hoon.hoon | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/pkg/arvo/sys/hoon.hoon b/pkg/arvo/sys/hoon.hoon
index c99289c90b..c28db59392 100644
--- a/pkg/arvo/sys/hoon.hoon
+++ b/pkg/arvo/sys/hoon.hoon
@@ -226,6 +226,33 @@
     *   (add (mod b 2) (mul $(b (div b 2)) 2))
   ==
 ::
+++  pin
+  ~/  %pin
+  ::    sub axis test
+  ::
+  ::  checks whether {b} addresses a subtree of the tree addressed by {a}.
+  |=  [a=@ b=@]
+  ?<  =(0 a)
+  ?<  =(0 b)
+  |-  ^-  ?
+  ?:  =(a 1)  %&
+  ?:  =((cap a) (cap b))
+    $(a (mas a), b (mas b))
+  %|
+++  awl
+  ~/  %awl
+  ::    axis after axis
+  ::  computes the remainder of axis {b} when navigating to {a}.
+  ::  (crashes if not `(pin a b)`)
+  |=  [a=@ b=@]
+  ?<  =(0 a)
+  ?<  =(0 b)
+  |-  ^-  @
+  ?:  =(a 1)  b
+  ?:  =((cap a) (cap b))
+    $(a (mas a), b (mas b))
+  !!
+::
 ::  #  %containers
 ::
 ::    the most basic of data types