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