wyil.util.type

Class TypeAlgorithms

java.lang.Object

wyil.util.type.TypeAlgorithms

public final class TypeAlgorithms
extends Object

Contains various important algorithms for manipulating types. These were split out from wyil.lang.Type, as that class is already quite large. The most important algorithms contained in this class are:

• Type Intersection. Here, the intersection of two types is calculated. This is necessary for determining the updated type after a runtime type test. Essentially, we intersect the original type with the tested type to produce something new.

• Type Simplification. Here, a number of simplification rules are provided which reduce non-sensical forms into something sensible. For example, int|int is a non-sensical form, and should be simplified to just int.

NOTE: the algorithms contained in this file are ugly and difficult to follow. Do not touch them unless you absolutely know what you're doing!

Author:

David J. Pearce

Field Summary

Fields

Modifier and Type	Field and Description
static Comparator<Automaton.State>	DATA_COMPARATOR The data comparator is used in the type canonicalisation process.

Constructor Summary

Constructors

Constructor and Description
TypeAlgorithms()

Method Summary

Modifier and Type	Method and Description
static boolean	isContractive(Automaton automaton) Contractive types are types which cannot accept value because they have an unterminated cycle.
static void	simplify(Automaton automaton) Analyse an automaton and try to produce a version that is simpler but still equivalent.

Methods inherited from class java.lang.Object

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

Field Detail

DATA_COMPARATOR

public static final Comparator<Automaton.State> DATA_COMPARATOR

The data comparator is used in the type canonicalisation process. It is used to compare the supplementary data of states in automata representing types. Supplementary data is used for record kinds and

Constructor Detail

TypeAlgorithms

public TypeAlgorithms()

Method Detail

isContractive

public static boolean isContractive(Automaton automaton)

Contractive types are types which cannot accept value because they have an unterminated cycle. An unterminated cycle has no leaf nodes terminating it. For example, X<{X field}> is contractive, where as X<{null|X field}> is not.

This method returns true if the type is contractive, or contains a contractive subcomponent. For example, null|X<{X field}> is considered contracted.

Parameters:

type - --- type to test for contractivity.

Returns:

simplify

public static void simplify(Automaton automaton)

Analyse an automaton and try to produce a version that is simpler but still equivalent.

Parameters:

automaton - --- automaton to simplify.