urbit/base/pub/doc/hoon/runes/sm/smsg.md

semsig, ;~, %smsg

Monad composer

;! is a synthetic rune used to compose functions under a monad.

Produces

Twig: [%smsg p=(list beer)]

Sample

p is a ++list of ++beer.

Tall form

;~  p
  i.q
  i.t.q
  i.t.t.q
==

Wide form

;~(p i.q i.t.q i.t.t.q)

Irregular form

None

Examples

~zod/try=> =cmp |=([a=tape b=$+(char tape)] `tape`?~(a ~ (weld (b i.a) t.a)))
~zod/try=> ;~(cmp trip)
<1.xef [a=@ <374.hzt 100.kzl 1.ypj %164>]>
~zod/try=> (;~(cmp trip) 'a')
"a"

;~ accepts a composer and a nonempty list of gates; at one gate, the composer is ignored, and the gate applied directly.

~zod/try=> (;~(cmp trip |=(a=@ ~[a a])) 'a')
"aa"
~zod/try=> (;~(cmp trip |=(a=@ ~[a a])) '')
""

For multiple gates, ;~ uses the composer to connect the gates in order.

~zod/try=> (;~(cmp trip ;~(cmp |=(a=@ ~[a a]) |=(a=@ <(dec a)>))) 'b')
"97b"
~zod/try=> (;~(cmp trip |=(a=@ ~[a a]) |=(a=@ <(dec a)>)) 'b')
"97b"
~zod/try=> (;~(cmp trip |=(a=@ ~[a a]) |=(a=@ <(dec a)>)) '')
""
~zod/try=> (;~(cmp trip |=(a=@ ~[a a]) |=(a=@ <(dec a)>)) 'a')
"96a"
~zod/try=> (;~(cmp trip |=(a=@ ~[a a]) |=(a=@ <(dec a)>)) 'acd')
"96acd"

Multiple gates are equivalent to stacked semsigs.

---

[~ 0]
~zod/try=> ((slat %p) '~nec')
[~ 1]
~zod/try=> ((slat %p) 'nec')
~
~zod/try=> ;~(biff (slat %p))
<1.ags [txt=@ta <1.wqj [mod=@tas <374.hzt 100.kzl 1.ypj %164>]>]>
~zod/try=> (;~(biff (slat %p)) '~zod')
[~ 0]
~zod/try=> (;~(biff (slat %p)) '~')
~
~zod/try=> (;~(biff (slat %p)) '~nec')
[~ 1]

More commonly, this can be used for unit composition. (slat %p) parses cords in phonetic base, failure case: invalid text

~zod/try=> (mo [~nec 12] [~tug 16] ~)
{[p=~nec q=12] [p=~tug q=16]}
~zod/try=> ~(get by (mo [~nec 12] [~tug 16] ~)) 
<1.yvn [* <18.wzi [a=nlr([p=@p q=@ud]) <374.hzt 100.kzl 1.ypj %164>]>]>
~zod/try=> =yaz ~(get by (mo [~nec 12] [~tug 16] ~)) 
~zod/try=> (yaz ~nec)
[~ 12]
~zod/try=> (yaz ~zod)
~
~zod/try=> (yaz ~tug)
[~ 16]

mo makes a map, and +-get:by is used to retrieve values from one, failure case: no such key

~zod/try=> (;~(biff (slat %p) yaz) '~zod')
~
~zod/try=> (;~(biff (slat %p) yaz) '~nec')
[~ 12]
~zod/try=> (;~(biff (slat %p) yaz) 'tug')
~
~zod/try=> (;~(biff (slat %p) yaz) '~tug')
[~ 16]

~zod/try=> (;~(biff (slat %p) yaz |=(a=@ud [~ (add 100 a)])) '~nec')
[~ 112]
~zod/try=> (;~(biff (slat %p) yaz |=(a=@ud [~ (add 100 a)])) '~zod')
~
~zod/try=> (;~(biff (slat %p) yaz |=(a=@ud [~ (add 100 a)])) 'mal')
~

These can be combined with biff, which connects a previous succeeded unit result by a gate that itself produces a unit from it.

---

~zod/try=> (hep [1 1] "")
[p=[p=1 q=1] q=~]
~zod/try=> (hep [1 1] "-")
[p=[p=1 q=2] q=[~ [p=~~- q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(hep [1 1] "-")
[p=[p=1 q=2] q=[~ [p='-' q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(hep [1 1] "?")
[p=[p=1 q=1] q=~]
~zod/try=> (lus [1 1] "+")
[p=[p=1 q=2] q=[~ [p=~~~2b. q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(lus [1 1] "+")
[p=[p=1 q=2] q=[~ [p='+' q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(lus [1 1] "++")
[p=[p=1 q=2] q=[~ [p='+' q=[p=[p=1 q=2] q="+"]]]]
~zod/try=> `(like cord)`(lus [1 1] " +")
[p=[p=1 q=1] q=~]
~zod/try=> `(like cord)`(;~(pose hep lus) [1 1] "?")
[p=[p=1 q=1] q=~]
~zod/try=> `(like cord)`(;~(pose hep lus) [1 1] "-")
[p=[p=1 q=2] q=[~ [p='-' q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(;~(pose hep lus) [1 1] "+")
[p=[p=1 q=2] q=[~ [p='+' q=[p=[p=1 q=2] q=""]]]]
~zod/try=> `(like cord)`(;~(pose hep lus) [1 1] "a")
[p=[p=1 q=1] q=~]
~zod/try=> `(like cord)`(;~(pose hep lus) [1 1] "-+")
[p=[p=1 q=2] q=[~ [p='-' q=[p=[p=1 q=2] q="+"]]]]
~zod/try=> `(like ,[cord cord])`(;~(plug hep lus) [1 1] "+")
[p=[p=1 q=1] q=~]
~zod/try=> `(like ,[cord cord])`(;~(plug hep lus) [1 1] "-+")
[p=[p=1 q=3] q=[~ [p=['-' '+'] q=[p=[p=1 q=3] q=""]]]]
~zod/try=> `(like ,[cord cord])`(;~(plug hep lus) [1 1] "-+ ")
[p=[p=1 q=3] q=[~ [p=['-' '+'] q=[p=[p=1 q=3] q=" "]]]]

Most prominently, however, ;~ is used for combinator parsers, composing [rule]s in various ways

See parsing sections 2eA - 2eH, and specifically section 2eD, for more information.