wytp.types

Class TypeSystem

java.lang.Object

wytp.types.TypeSystem

public class TypeSystem
extends Object

Field Summary

Fields

Modifier and Type	Field and Description
static TypeInferer.Environment	NULL_ENVIRONMENT The "null" environment provides a simple environment which simply falls back to using the declared type for a given variable.

Constructor Summary

Constructors

Constructor and Description
TypeSystem(wybs.lang.Build.Project project)

Method Summary

Modifier and Type	Method and Description
Formula	extractInvariant(WyalFile.Type type, WyalFile.Expr root) Extracting the invariant (if any) from a given type.
WyalFile.Type.Array	extractReadableArray(WyalFile.Type type) Extract the readable array type from a given type.
WyalFile.Type.Record	extractReadableRecord(WyalFile.Type type) For a given type, extract its effective record type.
WyalFile.Type.Reference	extractReadableReference(WyalFile.Type type) Extract the readable reference type from a given type.
WyalFile.Type	inferType(TypeInferer.Environment environment, WyalFile.Expr expression) Get the type inferred for a given expression in a given environment.
boolean	isRawSubtype(WyalFile.Type lhs, WyalFile.Type rhs) Determine whether one type is a raw subtype of another.
<T extends WyalFile.Declaration.Named> List<T>	resolveAll(wybs.util.AbstractCompilationUnit.Name name, Class<T> kind)
<T extends WyalFile.Declaration.Named> T	resolveExactly(wybs.util.AbstractCompilationUnit.Name name, Class<T> kind)
WyalFile.Type	simplify(WyalFile.Type type)

Methods inherited from class java.lang.Object

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

Field Detail

NULL_ENVIRONMENT

public static final TypeInferer.Environment NULL_ENVIRONMENT

The "null" environment provides a simple environment which simply falls back to using the declared type for a given variable.

Constructor Detail

TypeSystem

public TypeSystem(wybs.lang.Build.Project project)

Method Detail

isRawSubtype

public boolean isRawSubtype(WyalFile.Type lhs,
                            WyalFile.Type rhs)
                     throws wybs.lang.NameResolver.ResolutionError

Determine whether one type is a raw subtype of another. Specifically, whether the raw type of rhs is a subtype of lhs's raw type (i.e. "⌊lhs⌋ :> ⌊rhs⌋"). The raw type is that which ignores any type invariants involved. Thus, one must be careful when interpreting the meaning of this operation. Specifically, "⌊lhs⌋ :> ⌊rhs⌋" does not imply that "lhs :> rhs" holds. However, if "⌊lhs⌋ :> ⌊rhs⌋" does not hold, then it does follow that "lhs :> rhs" also does not hold.

Depending on the exact language of types involved, this can be a surprisingly complex operation. For example, in the presence of union, intersection and negation types, the subtype algorithm is surprisingly intricate.

Parameters:

lhs - The candidate "supertype". That is, lhs's raw type may be a supertype of rhs's raw type.

rhs - The candidate "subtype". That is, rhs's raw type may be a subtype of lhs's raw type.

Returns:

Throws:

wybs.lang.NameResolver.ResolutionError - Occurs when a nominal type is encountered whose name cannot be resolved properly. For example, it resolves to more than one possible matching declaration, or it cannot be resolved to a corresponding type declaration.

extractReadableRecord

public WyalFile.Type.Record extractReadableRecord(WyalFile.Type type)
                                           throws wybs.lang.NameResolver.ResolutionError

For a given type, extract its effective record type. For example, the type ({int x, int y}|{int x, int z}) has effective record type {int x, ...}. The following illustrates some more cases:

 {int x, int y} | null    ==> null
 {int x, int y} | {int x} ==> null
 {int x, int y} | {int x, bool y} ==> {int x, int|bool y}
 {int x, int y} & null    ==> null
 {int x, int y} & {int x} ==> null
 {int x, int y} & {int x, int|bool y} ==> {int x, int y}
 

Parameters:

type -

Returns:

Throws:

wybs.lang.NameResolver.ResolutionError

extractReadableArray

public WyalFile.Type.Array extractReadableArray(WyalFile.Type type)
                                         throws wybs.lang.NameResolver.ResolutionError

Extract the readable array type from a given type. For example, the type (int[])|(bool[]) has a readable array type of (int|bool)[].

Parameters:

type -

Returns:

Throws:

wybs.lang.NameResolver.ResolutionError

extractReadableReference

public WyalFile.Type.Reference extractReadableReference(WyalFile.Type type)
                                                 throws wybs.lang.NameResolver.ResolutionError

Extract the readable reference type from a given type. This is relatively straightforward. For example, &int is extracted as &int. However, (&int)|(&bool) is not extracted as as &(int|bool).

Parameters:

type -

Returns:

Throws:

wybs.lang.NameResolver.ResolutionError

extractInvariant

public Formula extractInvariant(WyalFile.Type type,
                                WyalFile.Expr root)
                         throws wybs.lang.NameResolver.ResolutionError

Extracting the invariant (if any) from a given type. For example, consider the following type declaration:

 type nat is (int x) where x >= 0
 

Then, extracting the invariant from type nat gives x >= 0. Likewise, extracting the invariant from the type bool|int gives the invariant (x is int) ==> (x >= 0). Finally, extracting the invariant from the type nat[] gives the invariant forall(int i).(0 <= i && i < |xs| ==> xs[i] >= 0).

Throws:

wybs.lang.NameResolver.ResolutionError

inferType

public WyalFile.Type inferType(TypeInferer.Environment environment,
                               WyalFile.Expr expression)
                        throws wybs.lang.NameResolver.ResolutionError

Get the type inferred for a given expression in a given environment.

Parameters:

environment -

expression -

Returns:

Throws:

wybs.lang.NameResolver.ResolutionError - Occurs when a particular named type cannot be resolved.

resolveExactly

public <T extends WyalFile.Declaration.Named> T resolveExactly(wybs.util.AbstractCompilationUnit.Name name,
                                                               Class<T> kind)
                                                        throws wybs.lang.NameResolver.ResolutionError

Throws:

wybs.lang.NameResolver.ResolutionError

resolveAll

public <T extends WyalFile.Declaration.Named> List<T> resolveAll(wybs.util.AbstractCompilationUnit.Name name,
                                                                 Class<T> kind)
                                                          throws wybs.lang.NameResolver.ResolutionError

Throws:

wybs.lang.NameResolver.ResolutionError

simplify

public WyalFile.Type simplify(WyalFile.Type type)