urbit/pub/docs/dev/hoon/library/2ee.md

section 2eE, parsing (composers)

++bass

++  bass
  |*  [wuc=@ tyd=_rule]
  %+  cook
    |=  waq=(list ,@)
    %+  roll
      waq
    =|([p=@ q=@] |.((add p (mul wuc q))))
  tyd
::

Parser modifier: LSB ordered list as atom of a base.

wuc is an atom.

tyd is a rule.

~zod/try=> (scan "123" (bass 10 (star dit)))
q=123
~zod/try=> (scan "123" (bass 8 (star dit)))
q=83
~zod/try=> `@ub`(scan "123" (bass 8 (star dit)))
0b101.0011

---

++boss

++  boss
  |*  [wuc=@ tyd=_rule]
  %+  cook
    |=  waq=(list ,@)
    %+  reel
      waq
    =|([p=@ q=@] |.((add p (mul wuc q))))
  tyd
::

Parser modifier: LSB ordered list as atom of a base.

wuc is an atom.

tyd is a rule.

~zod/try=> (scan "123" (boss 10 (star dit)))
q=321
~zod/try=> `@t`(scan "bam" (boss 256 (star alp)))
'bam'
~zod/try=> `@ux`(scan "bam" (boss 256 (star alp)))
0x6d.6162

---

++ifix

++  ifix
  |*  [fel=[p=_rule q=_rule] hof=_rule]
  ;~(pfix p.fel ;~(sfix hof q.fel))
::

Parser modifier: surround with pair of rules, output of which is discarded.

fel is a pair of rules.

hof is a rule.

~zod/try=> (scan "-40-" (ifix [hep hep] dem))
q=40
~zod/try=> (scan "4my4" (ifix [dit dit] (star alf)))
"my"

---

++more

++  more
  |*  [bus=_rule fel=_rule]
  ;~(pose (most bus fel) (easy ~))
::

Parser modifier: using a delimiter rule, parse a list of matches.

bus is a rule.

fel is a rule.

~zod/try=> (scan "" (more ace dem))
~
~zod/try=> (scan "40 20" (more ace dem))
[q=40 ~[q=20]]
~zod/try=> (scan "40 20 60 1 5" (more ace dem))
[q=40 ~[q=20 q=60 q=1 q=5]]

---

++most

++  most
  |*  [bus=_rule fel=_rule]
  ;~(plug fel (star ;~(pfix bus fel)))
::

Parser modifier: using a delimiter rule, parse a list of at least one match.

bus is a rule.

fel is a rule.

~zod/try=> (scan "40 20" (most ace dem))
[q=40 ~[q=20]]
~zod/try=> (scan "40 20 60 1 5" (most ace dem))
[q=40 ~[q=20 q=60 q=1 q=5]]
~zod/try=> (scan "" (most ace dem))
! {1 1}
! exit

---

++plus

++  plus  |*(fel=_rule ;~(plug fel (star fel)))

Parser modifier: parse list of at least one match

fel is a rule.

~zod/try=> (scan ">>>>" (cook lent (plus gar)))
4
~zod/try=> (scan "-  - " (plus ;~(pose ace hep)))
[~~- "  - "]
~zod/try=> `tape`(scan "-  - " (plus ;~(pose ace hep)))
"-  - "
~zod/try=> `(pole ,@t)`(scan "-  - " (plus ;~(pose ace hep)))
['-' [' ' [' ' ['-' [' ' ~]]]]]

---

++slug

++  slug
  |*  raq=_|*([a=* b=*] [a b])
  |*  [bus=_rule fel=_rule]
  ;~((comp raq) fel (stir rud raq ;~(pfix bus fel)))
::

Parser modifier: By composing with a gate, parse a delimited list of matches.

bus is a rule.

fel is a rule.

~zod/try=> (scan "20+5+110" ((slug add) lus dem))
135
~zod/try=> `@t`(scan "a b c" ((slug |=(a=[@ @t] (cat 3 a))) ace alp))
'abc'

---

++star

++  star                                                ::  0 or more times
  |*  fel=_rule
  (stir `(list ,_(wonk *fel))`~ |*([a=* b=*] [a b]) fel)

Parser modifier: parse list of matches.

fel is a rule.

    ~zod/try=> (scan "aaaaa" (just 'a'))
    ! {1 2}
    ! 'syntax-error'
    ! exit
    ~zod/try=> (scan "aaaaa" (star (just 'a')))
    "aaaaa"
    ~zod/try=> (scan "abcdef" (star (just 'a')))
    ! {1 2}
    ! 'syntax-error'
    ! exit
    ~zod/try=> (scan "abcabc" (star (jest 'abc')))
    <|abc abc|>
    ~zod/try=> (scan "john smith" (star (shim 0 200)))
    "john smith"

---