BacktrackScanner

java.lang.Object
- easyIO.BacktrackScanner

Direct Known Subclasses:

Scanner
```
public class BacktrackScanner
extends java.lang.Object
```
A scanner class that, unlike java.util.Scanner, supports arbitrary lookahead and backtracking. The caller can use mark() to set some number of marks in the input stream, then accept() to erase the previous mark or abort() to roll back to (and erase) the previous mark. The marks function as a stack of previous points in the input. The class also allows reading a stream that is spread across multiple input sources, and keeps track of the current source, current line number, and current position within the line. Arbitrary lookahead is allowed, but the space consumed by a scanner is proportional to the number of chars between the first mark and last lookahead position.

See Also:

easyIO.Scanner

Nested Class Summary

Nested Classes
Modifier and Type	Class and Description
`static class`	`BacktrackScanner.Location` An input character along with information about the source of the character, and its line number and position within the line.

Constructor Summary

Constructors
Constructor and Description

BacktrackScanner()

Constructors
Constructor and Description
`BacktrackScanner()`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`abort()` Roll the input position back to the most recent mark, and erase the mark, effectively restarting scanning from that position.
`void`	`accept()` Effect: Erase the previous mark from the input, effectively accepting all input up to the current position.
`void`	`advance()` Advance past the next character, if any.
`void`	`appendSource(java.io.Reader r, java.lang.String name)` Add r to the input stream after existing inputs.
`int`	`charPos()`
`void`	`close()`
`int`	`depth()` The current number of marks.
`void`	`dump(java.lang.StringBuilder w)` Dump the state of the scanner to w in a human-readable form.
`BacktrackScanner.Location`	`getMarkLocation()` Location in input source of the last mark.
`java.lang.String`	`getToken()` Return a string containing the characters from the most recent mark to the current position.
`boolean`	`hasNext()` Whether there is a character ahead in input.
`void`	`includeSource(java.io.Reader r, java.lang.String name)` Add r to the input stream ahead of any existing inputs.
`boolean`	`invariant()`
`int`	`lineNo()`
`BacktrackScanner.Location`	`location()` Location in input source of the current position.
`void`	`mark()` Add a mark at the current position.
`char`	`next()` Read the next character from the stream.
`int`	`peek()` The next character ahead in the input.
`java.lang.String`	`source()`
`void`	`string(java.lang.String s)` Scan the characters of string s from the input.
`java.lang.String`	`toString()`

Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - BacktrackScanner
```
public BacktrackScanner()
```
- Method Detail
  - invariant
```
public boolean invariant()
```
  - dump
```
public void dump(java.lang.StringBuilder w)
```
    Dump the state of the scanner to w in a human-readable form.
  - close
```
public void close()
           throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - source
```
public java.lang.String source()
```
  - lineNo
```
public int lineNo()
```
  - charPos
```
public int charPos()
```
  - includeSource
```
public void includeSource(java.io.Reader r,
                          java.lang.String name)
```
    Add r to the input stream ahead of any existing inputs.
  - appendSource
```
public void appendSource(java.io.Reader r,
                         java.lang.String name)
```
    Add r to the input stream after existing inputs.
  - hasNext
```
public boolean hasNext()
```
    Whether there is a character ahead in input.
  - peek
```
public int peek()
```
    The next character ahead in the input. Equivalent to begin(); c = next(); abort(); return c;
  - location
```
public BacktrackScanner.Location location()
```
    Location in input source of the current position.
  - getMarkLocation
```
public BacktrackScanner.Location getMarkLocation()
```
    Location in input source of the last mark.
  - mark
```
public void mark()
```
    Add a mark at the current position.
  - accept
```
public void accept()
```
    Effect: Erase the previous mark from the input, effectively accepting all input up to the current position.
  - depth
```
public int depth()
```
    The current number of marks. Exposed for use in assertions, so client code can check that matching mark()...accept() calls occur at the same depth.
  - getToken
```
public java.lang.String getToken()
```
    Return a string containing the characters from the most recent mark to the current position.
  - abort
```
public void abort()
```
    Roll the input position back to the most recent mark, and erase the mark, effectively restarting scanning from that position.
  - advance
```
public void advance()
```
    Advance past the next character, if any. Do nothing if at end of input.
  - next
```
public char next()
          throws EOF
```
    Read the next character from the stream.
    
    Throws:
    
    EOF
  - string
```
public void string(java.lang.String s)
            throws UnexpectedInput
```
    Scan the characters of string s from the input.
    
    Throws:
    
    UnexpectedInput - if something other than the expected characters are encountered.
  - toString
```
public java.lang.String toString()
```
    Overrides:
    
    toString in class java.lang.Object

Class BacktrackScanner

Nested Class Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

BacktrackScanner

Method Detail

invariant

dump

close

source

lineNo

charPos

includeSource

appendSource

hasNext

peek

location

getMarkLocation

mark

accept

depth

getToken

abort

advance

next

string

toString