more flexible merge arguments

cat/hood/merge.hoon

@@ -2,11 +2,32 @@
 ::::  /hoon/merge/hood/cat
   ::
 /?  314
+!:
+|%
+++  beaky  ,[span span span ~]
+++  sorc  ?([bek=beaky ~] [her=@p sud=@tas ~])
+--
 ::
 ::::
   !:
-|=  $:  [now=@da eny=@uvI bec=beak]
-        [[syd=@tas her=@p sud=@tas gem=?([?(%auto germ) ~] ~)] ~]
+|=  $:  [now=@da eny=@uvI bek=beak]
+        [arg=[?(sorc [syd=$|(desk beaky) sorc])] opt=(map ,%gem germ)]
     ==
-:-  %kiln-merge
-[syd her sud ?~(gem %auto -.gem)]
+=*  our  p.bek
+|^  :-  %kiln-merge
+    ^-  [syd=desk her=ship sud=desk gem=?(germ %auto)]
+    =+  gem=(fall (~(get by opt) %gem) %auto)
+    ?-  arg
+      [@ @ ~]    =+(arg [sud ?.(=(our her) her (sein her)) sud gem])
+      [^ ~]      =+((pars bek.arg) [dez ?.(=(our who) who (sein who)) dez gem])
+      [* @ @ ~]  [(pars-src syd.arg) =+(arg [her sud gem])]
+      [* ^ ~]    [(pars-src syd.arg) =+((pars bek.arg) [who dez gem])]
+    ==
+++  pars  |=(a=beaky =+((need (tome a)) `[who=ship dez=desk]`[p q]))
+++  pars-src
+  |=  syd=$|(desk beaky)
+  ?@  syd  syd
+  =+  (pars syd)
+  ~|  [%into-foreign who `path`syd]
+  ?>(=(our who) dez)
+--