# 4g: Parsing (Outside Caller)

## `+rash` <a href="#rash" id="rash"></a>

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` <a href="#rose" id="rose"></a>

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` <a href="#rush" id="rush"></a>

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` <a href="#rust" id="rust"></a>

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` <a href="#scan" id="scan"></a>

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
```

***