# 4g: Parsing (Outside Caller)
## `+rash`
Parse or crash.
Parse a `$cord` with a given `$rule` and crash if the `$cord` isn't entirely parsed.
#### Accepts
`.naf` is an `$atom`.
`.sab` is a `$rule`.
#### Produces
The value of the parse result, or crash.
#### Source
```hoon
++ rash |*([naf=@ sab=rule] (scan (trip naf) sab))
```
#### Examples
```
> (rash 'I was the world in which I walked, and what I saw' (star (shim 0 200)))
"I was the world in which I walked, and what I saw"
```
```
> (rash 'abc' (just 'a'))
! {1 2}
! 'syntax-error'
! exit
```
```
> (rash 'abc' (jest 'abc'))
'abc'
```
```
> (rash 'abc' (jest 'ab'))
! {1 3}
! 'syntax-error'
! exit
```
***
## `+rose`
Parse to each.
Parse `$tape` `.los` with `$rule` `sab`, producing an `(each @ud (unit *))`. If `.los` was not fully consumed, the result is `%.n` and `.p` contains the column number before failure occurred. If `.los` was fully consumed, the result is `%.y` and `.p` contains either `sab`'s result in a `+unit`, or a null `+unit` if parsing failed.
#### Accepts
`.los` is a `$tape`.
`.sab` is a `$rule`.
#### Produces
`(each @ud (unit *))`, where the `*` is whatever type the `$rule` produces.
#### Source
```hoon
++ rose |* [los=tape sab=rule]
=+ vex=(sab [[1 1] los])
=+ len=(lent los)
?. =(+(len) q.p.vex) [%| p=(dec q.p.vex)]
?~ q.vex
[%& p=~]
[%& p=[~ u=p.u.q.vex]]
```
#### Examples
```
> (rose "!" zap)
[%.y p=[~ u='!']]
```
```
> (rose "?" zap)
[%.n p=0]
```
```
> (rose "!?" zap)
[%.n p=1]
```
```
> (rose "!" ;~(plug zap fail))
[%.y p=~]
```
***
## `+rush`
Parse or null.
Parse an `$atom` with a given `$rule` and produce null if the `$cord` isn't entirely parsed.
#### Accepts
`.naf` is an `$atom`.
`.sab` is a `$rule`.
#### Produces
The value of the parse result, or null.
#### Source
```hoon
++ rush |*([naf=@ sab=rule] (rust (trip naf) sab))
```
#### Examples
```
> (rush 'I was the world in which I walked, and what I saw' (star (shim 0 200)))
[~ "I was the world in which I walked, and what I saw"]
```
```
> (rush 'abc' (just 'a'))
~
```
```
> (rush 'abc' (jest 'abc'))
[~ 'abc']
```
```
> (rush 'abc' (jest 'ac'))
~
```
```
> (rush 'abc' (jest 'ab'))
~
```
***
## `+rust`
Parse `$tape` or null.
Parse a `$tape` with a given `$rule` and produce null if the `$tape` isn't entirely parsed.
#### Accepts
`.los` is a `$tape`.
`.sab` is a `$rule`.
#### Produces
A `(unit *)`, where `*` is the type produced by `.sab`.
#### Source
```hoon
++ rust |* [los=tape sab=rule]
=+ vex=((full sab) [[1 1] los])
?~(q.vex ~ [~ u=p.u.q.vex])
```
#### Examples
```
> (rust "I was the world in which I walked, and what I saw" (star (shim 0 200)))
[~ "I was the world in which I walked, and what I saw"]
```
```
> (rust "Or heard or felt came not but from myself;" (star (shim 0 200)))
[~ "Or heard or felt came not but from myself;"]
```
```
> (rust "And there I found myself more truly and more strange." (jest 'And there I'))
~
```
***
## `+scan`
Parse `$tape` or crash.
Parse a `$tape` with a given `$rule` and crash if the `$tape` isn't entirely parsed.
#### Accepts
`.los` is a `$tape`.
`.sab` is a `$rule`.
#### Produces
Either the type produced by your parsing rules or a crash.
#### Source
```hoon
++ scan |* [los=tape sab=rule]
=+ vex=((full sab) [[1 1] los])
?~ q.vex
~_ (show [%m '{%d %d}'] p.p.vex q.p.vex ~)
~_(leaf+"syntax error" !!)
p.u.q.vex
```
#### Examples
```
> (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"
```
```
> (scan "Or heard or felt came not but from myself;" (star (shim 0 200)))
"Or heard or felt came not but from myself;"
```
```
> (scan "And there I found myself more truly and more strange." (jest 'And there I'))
! {1 12}
! 'syntax-error'
! exit
```
***
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