net.sourceforge.czt.animation.eval

Class Envir

java.lang.Object

net.sourceforge.czt.animation.eval.Envir

public class Envir
extends Object

An Environment is conceptually a mapping from variable names (ZName) to values (Expr). However, it can also contain additional information about each name, such as type information. This data structure is designed to allow environments to be extended in a non-destructive way. This is why add() returns a new environment. TODO: think more about the semantics of the equals. Should the order matter? Should duplicate names matter? But is equals used anywhere, apart from unit tests?

Field Summary

Fields

Modifier and Type	Field and Description
protected net.sourceforge.czt.z.ast.Expr	expr_
protected net.sourceforge.czt.z.ast.ZName	name_
protected Envir	nextEnv

Constructor Summary

Constructors

Constructor and Description
Envir() Create an empty Envir

Method Summary

Modifier and Type	Method and Description
Envir	deepCopy() Returns a copy of this environment, with no values shared.
Set<net.sourceforge.czt.z.ast.ZName>	definedSince(Envir env0) Return the set of newly defined names.
boolean	equals(Object obj) Two environments are equal if they contain the same names and values, in exactly the same order.
int	hashCode()
Envir	hide(net.sourceforge.czt.z.ast.ZName name) Hides the given name, so the the environment *appears* not to include that name.
boolean	isDefined(net.sourceforge.czt.z.ast.ZName want) See if a name is defined in the Environment.
boolean	isDefinedSince(Envir env0, net.sourceforge.czt.z.ast.ZName want) See if a name is recently defined in the Environment.
net.sourceforge.czt.z.ast.Expr	lookup(net.sourceforge.czt.z.ast.ZName want) Lookup the value of a name in the Environment.
protected void	pairToString(StringBuffer result)
Envir	plus(net.sourceforge.czt.z.ast.ZName name, net.sourceforge.czt.z.ast.Expr value) Create a new Envir which equals this one, plus an extra name,value pair.
Envir	plusAll(net.sourceforge.czt.z.ast.BindExpr binding) Creates an environment which extends this one by adding all the name==expr pairs in binding.
static boolean	sameName(net.sourceforge.czt.z.ast.ZName a, net.sourceforge.czt.z.ast.ZName b)
void	setValue(net.sourceforge.czt.z.ast.ZName name, net.sourceforge.czt.z.ast.Expr newvalue) Update the value of a name in the Environment.
String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

nextEnv

protected Envir nextEnv

name_

protected net.sourceforge.czt.z.ast.ZName name_

expr_

protected net.sourceforge.czt.z.ast.Expr expr_

Constructor Detail

Envir

public Envir()

Create an empty Envir

Method Detail

lookup

public net.sourceforge.czt.z.ast.Expr lookup(net.sourceforge.czt.z.ast.ZName want)

Lookup the value of a name in the Environment.

Returns:

The value may be null.

Throws:

EvalException - if want is not defined in this environment.

sameName

public static boolean sameName(net.sourceforge.czt.z.ast.ZName a,
                               net.sourceforge.czt.z.ast.ZName b)

definedSince

public Set<net.sourceforge.czt.z.ast.ZName> definedSince(Envir env0)

Return the set of newly defined names.

isDefinedSince

public boolean isDefinedSince(Envir env0,
                              net.sourceforge.czt.z.ast.ZName want)

See if a name is recently defined in the Environment.

Returns:

true if the name is defined in this environment, but not in env0.

isDefined

public boolean isDefined(net.sourceforge.czt.z.ast.ZName want)

See if a name is defined in the Environment.

Returns:

true if the name exists, false if it does not exist.

setValue

public void setValue(net.sourceforge.czt.z.ast.ZName name,
                     net.sourceforge.czt.z.ast.Expr newvalue)

Update the value of a name in the Environment. WARNING: this destructively changes the Environment and may change other environments that share parts of this environment.

Parameters:

name - This name must already exist in the environment.

newvalue - The new value for name.

plus

public Envir plus(net.sourceforge.czt.z.ast.ZName name,
                  net.sourceforge.czt.z.ast.Expr value)

Create a new Envir which equals this one, plus an extra name,value pair. It is quite common to set the value to null, which means that the actual value of that name will be set later, using the setValue method. Typically, the name,value pair is created once, then setValue is used to give the name many different values during the search for a solution to some predicate.

Parameters:

name - The name to add.

value - The value to which name will be bound. Can be null.

Returns:

The new extended environment

plusAll

public Envir plusAll(net.sourceforge.czt.z.ast.BindExpr binding)

Creates an environment which extends this one by adding all the name==expr pairs in binding.

hide

public Envir hide(net.sourceforge.czt.z.ast.ZName name)

Hides the given name, so the the environment *appears* not to include that name.

Parameters:

name -

Returns:

hashCode

public int hashCode()

Overrides:

hashCode in class Object

equals

public boolean equals(Object obj)

Two environments are equal if they contain the same names and values, in exactly the same order.

Overrides:

equals in class Object

toString

public String toString()

Overrides:

toString in class Object

pairToString

protected void pairToString(StringBuffer result)

deepCopy

public Envir deepCopy()

Returns a copy of this environment, with no values shared. This is sometimes necessary when an expression with free variables (eg. SetComp) is being passed outside of its scope, so the value of those variables needs to be copied and frozen.