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

section 2eI, parsing (external)

++rash

Parse or crash

++  rash  |*([naf=@ sab=_rule] (scan (trip naf) sab))   ::

Parse a cord with a given rule and crash if the cord isn't entirely parsed.

naf is an atom.

sab is a rule.

~zod/try=> (rash 'I was the world in which I walked, and what I saw' (star (shim 0 200)))
"I was the world in which I walked, and what I saw"
~zod/try=> (rash 'abc' (just 'a'))
! {1 2}
! 'syntax-error'
! exit
~zod/try=> (rash 'abc' (jest 'abc'))
'abc'
`~zod/try=> (rash 'abc' (jest 'ab'))
! {1 3}
! 'syntax-error'
! exit

---

++rush

Parse or null

++  rush  |*([naf=@ sab=_rule] (rust (trip naf) sab))

Parse a given with a given rule and produce null if the cord isn't entirely parsed.

naf is an atom.

sab is a rule.

    ~zod/try=> (rush 'I was the world in which I walked, and what I saw' (star (shim 0 200)))
    [~ "I was the world in which I walked, and what I saw"]
    ~zod/try=> (rush 'abc' (just 'a'))
    ~
    ~zod/try=> (rush 'abc' (jest 'abc'))
    [~ 'abc']
    ~zod/try=> (rush 'abc' (jest 'ac'))
    ~
    ~zod/try=> (rush 'abc' (jest 'ab'))
    ~

---

++rust

Parse tape or null

++  rust  |*  [los=tape sab=_rule]
          =+  vex=((full sab) [[1 1] los])
          ?~(q.vex ~ [~ u=p.u.q.vex])

Parse a tape with a given rule and produce null if the tape isn't entirely parsed.

los is a tape.

sab is a rule.

    ~zod/try=> (rust "I was the world in which I walked, and what I saw" (star (shim 0 200)))
    [~ "I was the world in which I walked, and what I saw"]
    ~zod/try=> (rust "Or heard or felt came not but from myself;" (star (shim 0 200)))
    [~ "Or heard or felt came not but from myself;"]
    ~zod/try=> (rust "And there I found myself more truly and more strange." (jest 'And there I'))
    ~

---

++scan

Parse tape or crash

++  scan  |*  [los=tape sab=_rule]
          =+  vex=((full sab) [[1 1] los])
          ?~  q.vex
            ~_  (show [%m '{%d %d}'] p.p.vex q.p.vex ~)
            ~|('syntax-error' !!)
          p.u.q.vex

Parse a tape with a given rule and crash if the tape isn't entirely parsed.

los is a tape.

sab is a rule.

    ~zod/try=> (scan "I was the world in which I walked, and what I saw" (star (shim 0 200)))
    "I was the world in which I walked, and what I saw"
    ~zod/try=> (scan "Or heard or felt came not but from myself;" (star (shim 0 200)))
    "Or heard or felt came not but from myself;"
    ~zod/try=> (scan "And there I found myself more truly and more strange." (jest 'And there I'))
    ! {1 12}
    ! 'syntax-error'
    ! exit