Package edu.harvard.seas.pl.abcdatalog.parser

Class DatalogParser

java.lang.Object

edu.harvard.seas.pl.abcdatalog.parser.DatalogParser

public final class DatalogParser
extends Object

A recursive descent parser for Datalog.

A Datalog program is a set of clauses, where each clause is in the form "a0 :- a1, ..., an." or "a0." and each ai is an atom of the form "pi" or "pi(t1, ..., tki)" for ki > 0 such that pi is a predicate symbol and each tj for 0 invalid input: '<' j invalid input: '<'= ki is a term (i.e. a constant or variable). Any variable in a0 must appear in at least one of ai, ..., an. Identifiers can contain letters, digits and underscores. Identifiers that begin with an upper case letter or an underscore are parsed as variables.

Method Summary

Modifier and Type	Method	Description
static void	main(String[] args)
static PositiveAtom	parseClauseAsPositiveAtom(DatalogTokenizer t)	Extracts an atom from the token stream.
static PositiveAtom	parsePositiveAtom(DatalogTokenizer t)	Attempts to extract an atom from the provided token stream.
static Set<Clause>	parseProgram(DatalogTokenizer t)	Generates an abstract syntax tree representation of the program described by the provided token stream.
static PositiveAtom	parseQuery(DatalogTokenizer t)	Attempts to extract an atom representation of the query described in the token stream.

Methods inherited from class java.lang.Object

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

Method Details

parseProgram

public static Set<Clause> parseProgram(DatalogTokenizer t)
                                throws DatalogParseException

Generates an abstract syntax tree representation of the program described by the provided token stream.

Parameters:

t - the token stream representation of program

Returns:

the AST of program

Throws:

DatalogParseException

parsePositiveAtom

public static PositiveAtom parsePositiveAtom(DatalogTokenizer t)
                                      throws DatalogParseException

Attempts to extract an atom from the provided token stream.

Parameters:

t - the token stream

Returns:

the atom

Throws:

DatalogParseException

parseQuery

public static PositiveAtom parseQuery(DatalogTokenizer t)
                               throws DatalogParseException

Attempts to extract an atom representation of the query described in the token stream.

Parameters:

t - the token stream

Returns:

the atom

Throws:

DatalogParseException

parseClauseAsPositiveAtom

public static PositiveAtom parseClauseAsPositiveAtom(DatalogTokenizer t)
                                              throws DatalogParseException

Extracts an atom from the token stream. The atom must be followed by a period.

Parameters:

t - the token stream

Returns:

the atom

Throws:

DatalogParseException

main

public static void main(String[] args)
                 throws DatalogParseException

Throws:

DatalogParseException