net.sourceforge.czt.animation.eval

Class ExprComparator

java.lang.Object

net.sourceforge.czt.animation.eval.ExprComparator

All Implemented Interfaces:

Serializable, Comparator<net.sourceforge.czt.z.ast.Expr>

public class ExprComparator
extends Object
implements Comparator<net.sourceforge.czt.z.ast.Expr>, Serializable

A comparator for evaluated Z expressions. The compare method defines a total order over evaluated Z expressions, such that the inferred equivalence relation is semantic equality of the Z expressions. This class uses the singleton pattern, so use the create() method to get an instance. TODO: handle members of given types. TODO: allow infinite sets to be compared against finite ones.

Author:

marku

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static int	EQUAL
static int	GREATERTHAN
static int	LESSTHAN

Method Summary

Modifier and Type	Method and Description
int	compare(net.sourceforge.czt.z.ast.Expr arg0, net.sourceforge.czt.z.ast.Expr arg1)
static ExprComparator	create()
static boolean	equalZ(net.sourceforge.czt.z.ast.Expr e1, net.sourceforge.czt.z.ast.Expr e2) A convenience method that checks equality according to Z semantics.
static int	exprType(Object e) Maps evaluated expressions into equivalence classes.
int	sign(int difference) Converts an integer difference into -1, 0, or +1.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Comparator

comparing, comparing, comparingDouble, comparingInt, comparingLong, equals, naturalOrder, nullsFirst, nullsLast, reversed, reverseOrder, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong

Field Detail

LESSTHAN

public static final int LESSTHAN

See Also:

Constant Field Values

EQUAL

public static final int EQUAL

See Also:

Constant Field Values

GREATERTHAN

public static final int GREATERTHAN

See Also:

Constant Field Values

Method Detail

create

public static ExprComparator create()

sign

public int sign(int difference)

Converts an integer difference into -1, 0, or +1.

equalZ

public static boolean equalZ(net.sourceforge.czt.z.ast.Expr e1,
                             net.sourceforge.czt.z.ast.Expr e2)

A convenience method that checks equality according to Z semantics. It is equivalent to create().compare(e1,e2) == 0.

Parameters:

e1 - An evaluated expression, such as an EvalSet

e2 - Another evaluated expression.

Returns:

true iff e1 and e2 are semantically equal.

compare

public int compare(net.sourceforge.czt.z.ast.Expr arg0,
                   net.sourceforge.czt.z.ast.Expr arg1)

Specified by:

compare in interface Comparator<net.sourceforge.czt.z.ast.Expr>

exprType

public static int exprType(Object e)

Maps evaluated expressions into equivalence classes. This is used to order expressions, from simplest to more complex. It must also respect the semantics of Z equality. For example, this means that all kinds of sets must be in the same equivalence class, even if they have different implementations.

Parameters:

e - The expression to classify.

Returns:

The (non-negative) equivalence class of the expression.

Throws:

RuntimeException - if it e is an unknown kind of Expr to ZLive, or if it is not fully evaluated.