edu.hws.jcm.data

Class ParserContext

java.lang.Object

edu.hws.jcm.data.ParserContext

All Implemented Interfaces:

Serializable

public class ParserContext
extends Object
implements Serializable

A ParserContext holds all the state data for a parsing operation, including the string that is being parsed, a pointer to the current position in that string, and the most recently parsed token from the string. The ParserContext object does the tokenization. Token types are retrieved by calling look() and next(). Attributes of the token are then available in the member variables tokenString, tokenObject, and tokenValue. You will probably only use this if you write a ParserExtension.

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Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
String	data The string that is being parsed.
static int	END_OF_STRING One of the possible token types returned by look() and next().
static int	IDENTIFIER One of the possible token types returned by look() and next().
static int	NUMBER One of the possible token types returned by look() and next().
static int	OPCHARS One of the possible token types returned by look() and next().
int	options The options from the Parser.
int	pos Current position in that string, indicating how many characters have been consumed.
ExpressionProgram	prog The ExpressionProgram that is being generated as the string is parsed.
protected SymbolTable	symbols The Parser's symbol table, which is used for looking up tokens of type IDENTIFIER.
int	token The most recently read token type, or NONE if that token has been consumed by a call to next().
MathObject	tokenObject If the most recently read token was of type IDENTIFIER, then this is the corresponding MathObject from the symbol table, or null if the identifier is not in the symbol table.
String	tokenString The substring of the parse string that corresponds to the most recently read token.
double	tokenValue If the most recently read token was of type NUMBER, then this is its numerical value.

Constructor Summary

Constructors

Constructor and Description
ParserContext(String data, int options, SymbolTable symbols) Create a ParserContext for parsing the data String, using the specified options and symbol table.

Method Summary

Modifier and Type	Method and Description
void	add(MathObject sym) Add a new MathObject to the symbol table.
MathObject	get(String name) Get the MathObject associated with name in the symbol table.
int	look() Look ahead at the next token in the data string, without consuming it.
void	mark() MathObjects added to the symbol table after a call to mark() will be removed by a later, matching call to revert().
int	next() Consume one token from the string.
void	revert()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

END_OF_STRING

public static final int END_OF_STRING

One of the possible token types returned by look() and next(). Represents the end of the string that is being parsed.

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Constant Field Values

NUMBER

public static final int NUMBER

One of the possible token types returned by look() and next(). Indicates aht the token is a number. The numerical value of the token is in the tokenValue member variable.

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Constant Field Values

IDENTIFIER

public static final int IDENTIFIER

One of the possible token types returned by look() and next(). The token is a word. If there is a MathObject in the symbol table associated with this word, then that object is in the tokenObject member variable. If not, tokenObject is null.

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Constant Field Values

OPCHARS

public static final int OPCHARS

One of the possible token types returned by look() and next(). Any other token besides end-of-string, number, or word. The only information about the token is the tokenString member variable. For some special operators (<> <= <=), the tokenString has two characters, but generally it has only one. Note that ** is translated to ^. Also, the special tokens "and", "or", and "not" are translated to type OPCHARS with tokenString equal to "&", "|", or "~" (but only if options & BOOLEANS is != 0).

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Constant Field Values

data

public String data

The string that is being parsed.

pos

public int pos

Current position in that string, indicating how many characters have been consumed.

prog

public ExpressionProgram prog

The ExpressionProgram that is being generated as the string is parsed. Note that while parsing a ConditionalExpression, the value of prog is temporarily changed. ParserExtensions might want to do something similar.

token

public int token

The most recently read token type, or NONE if that token has been consumed by a call to next(). The value NONE is never returned by look() or next().

tokenString

public String tokenString

The substring of the parse string that corresponds to the most recently read token. This can change when look() or next() is called.

tokenObject

public MathObject tokenObject

If the most recently read token was of type IDENTIFIER, then this is the corresponding MathObject from the symbol table, or null if the identifier is not in the symbol table.

tokenValue

public double tokenValue

If the most recently read token was of type NUMBER, then this is its numerical value.

options

public int options

The options from the Parser. Some of these options affect tokenization, such as whether BOOLEANS is enabled.

symbols

protected SymbolTable symbols

The Parser's symbol table, which is used for looking up tokens of type IDENTIFIER.

Constructor Detail

ParserContext

public ParserContext(String data,
                     int options,
                     SymbolTable symbols)

Create a ParserContext for parsing the data String, using the specified options and symbol table. A new ExpressionProgram is created to hold the program that will be generated from the string.

Method Detail

mark

public void mark()

MathObjects added to the symbol table after a call to mark() will be removed by a later, matching call to revert(). In the meantime, older symbols of the same name will only be hidden, not replaced, so they will still be there after the revert. It is important that a call to this routine is followed by a later call to revert! No error checking is done to make sure that this is true.

revert

public void revert()

get

public MathObject get(String name)

Get the MathObject associated with name in the symbol table.

add

public void add(MathObject sym)

Add a new MathObject to the symbol table.

next

public int next()

Consume one token from the string. The token type is returned. After this is called, attributes of the token can be obtained from the public member variables tokenString, tokenObject, and tokenValue. Note that the END_OF_STRING token is never really consumed and can be returned multiple times. Can throw a ParseError in the case of an illegal numeric token.

look

public int look()

Look ahead at the next token in the data string, without consuming it. Successive calls to look() will return the same token. (The token must be consumed by a call to next().) The token type is returned. After a call to look(), attributes of the token can be obtained from the public member variables tokenString, tokenObject, and tokenValue. Can throw a ParseError in the case of an illegal numeric token.