edu.mit.ai.psg.jevaES
Class EvalMethods

java.lang.Object
  |
  +--edu.mit.ai.psg.jevaES.EvalMethods

public class EvalMethods

extends Object

Centralized static methods for evaluating nodes while catching exceptions. Top level: evaluate(IExpressionNode) verifies type consistency before evaluating.

To evaluate subnodes, nodes call EvalMethods.eval(node, env) rather than calling the subnode eval method directly, so that when an error is thrown, this will wrap error in an EvaluatingError which identifies what node and env was being evaluated at the time. Similarly, nodes call EvalMethods.getType(IExpressionNode, IEnv) and EvalMethods.verifyTypes(IStatementNode, IEnv) rather than calling subnode methods directly so that when an error is thrown, this will wrap the error in a VerifyingError identifying node and env.

Evaluation may also throw other exceptions:

• AbruptCompletionException: exceptions used during correct operation of program, e.g., for throws, returns, breaks, continues. These should generally be caught only by nodes which receive the transfer of control (e.g., catch a throw), or at top level.
  • ThrowException: a valid exception generated at runtime according to JavaLangSpec1.0, e.g., via a throw statement.
  • ReturnException: evaluated node executed a return statement.
  • BreakException: evaluated node executed a break statement.
  • ContinueException: evaluated node executed a continue statement.
• VerifyingException: subclasses for non-continueable problems, a "compile-time error" in Java Language Specificiation 1.0.
  • IllegalTypeException: an incompatible type was encountered.
  • IllegalNameException: an undefined, ambiguous, or conflicting name was encountered.
  • IllegalConstructException: a Java construct was improperly formed, or used in an improper context
• EvaluatingError: An error occured while evaluating, due to a bug.
• VerifyingError: An error occurred while verifying, due to a bug.

See Also:

VerifyingException, IllegalTypeException, IllegalNameException, IllegalConstructException, AbruptCompletionException, ThrowException, ReturnException, BreakException, ContinueException, VerifyingError, EvaluatingError

Field Summary

static IEnv

defaultEnv

Method Summary

static Object	eval(IExpressionNode node) return the value of previously verified expression in root env.
static Object	eval(IExpressionNode enode, IEnv env) return the value of this previously verified expression in given env.
static IEnv	eval(IStatementNode node) return IEnv, extended by previously verified statement.
static IEnv	eval(IStatementNode snode, IEnv env) return env extended by this previously verified statement in given env.
static IStore	evalToStore(IExpressionStoreNode node) return IStore for getting or setting the location denoted by this previously verified expression in root env.
static IStore	evalToStore(IExpressionStoreNode esnode, IEnv env) return an IStore to get or set the location denoted by this previously verified expression in the given env.
static Object	evaluate(IExpressionNode node) verify types then evaluate node with default env
static Object	evaluate(IExpressionNode node, IEnv env) verify types then evaluate node with given env
static IEnv	evaluate(IStatementNode node) verify types then evaluate node with default env
static IEnv	evaluate(IStatementNode node, IEnv env) verify types then evaluate node with given env
static Class	getType(IExpressionNode node) return the Class representing the Java type of this expression in default env, after type checking subexpressions.
static Class	getType(IExpressionNode node, IEnv env) return Class representing Java type of this expression in given env after type checking subexpressions.
static boolean	isConstant(IExpressionNode node) return true if this expression has constant value in root env.
static boolean	isConstant(IExpressionNode node, IEnv env) return true if this expression has constant value in given env.
static Error	shouldNotHappen(String explain) prints stack trace of thread on System.err, returns new Error
static Error	shouldNotHappen(String explain, Throwable e) prints stack trace of e on System.err, returns new Error
static Error	shouldNotHappen(Throwable e) prints stack trace of e on System.err, returns new Error
static IEnv	verifyTypes(IStatementNode node)
static IEnv	verifyTypes(IStatementNode node, IEnv env) return IEnv, extended by this statement if it is a local declaration but without evaluating initializers, after verifying types.

Methods inherited from class java.lang.Object

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

Field Detail

defaultEnv

public static IEnv defaultEnv

Method Detail

evaluate

public static Object evaluate(IExpressionNode node)
                       throws VerifyingException,
                              ThrowException

verify types then evaluate node with default env

Returns:

value of expression evaluated in default env

Throws:

VerifyingException - if expression is illegal

ThrowException - if completes abruptly with an exception

evaluate

public static IEnv evaluate(IStatementNode node)
                     throws VerifyingException,
                            AbruptCompletionException

verify types then evaluate node with default env

Returns:

value of expression evaluated in default env

Throws:

VerifyingException - if statement is illegal

AbruptCompletionException - if completes abruptly

evaluate

public static Object evaluate(IExpressionNode node,
                              IEnv env)
                       throws VerifyingException,
                              ThrowException

verify types then evaluate node with given env

Returns:

value of expression evaluated in default env

Throws:

VerifyingException - if illegal expression

ThrowException - if completes abruptly with an exception

evaluate

public static IEnv evaluate(IStatementNode node,
                            IEnv env)
                     throws VerifyingException,
                            AbruptCompletionException

verify types then evaluate node with given env

Returns:

value of expression evaluated in default env

Throws:

VerifyingException - if illegal statement

AbruptCompletionException - if completes abruptly

getType

public static Class getType(IExpressionNode node)
                     throws VerifyingException

return the Class representing the Java type of this expression in default env, after type checking subexpressions.

Throws:

VerifyingException - if expression is illegal.

isConstant

public static boolean isConstant(IExpressionNode node)
                          throws VerifyingException

return true if this expression has constant value in root env.

Throws:

VerifyingException - if expression is illegal.

verifyTypes

public static IEnv verifyTypes(IStatementNode node)
                        throws VerifyingException

Returns:

IEnv, extended by this statement if it is a local declaration but without evaluating initializers, after verifying types.

Throws:

VerifyingException - if statement is illegal.

eval

public static Object eval(IExpressionNode node)
                   throws ThrowException

return the value of previously verified expression in root env.

Parameters:

previously - verified expression

Throws:

ThrowException - if completes abruptly with an exception

eval

public static IEnv eval(IStatementNode node)
                 throws AbruptCompletionException

return IEnv, extended by previously verified statement.

Parameters:

previously - verified statement

Throws:

AbruptCompletionException - if completes abruptly

evalToStore

public static IStore evalToStore(IExpressionStoreNode node)
                          throws ThrowException

return IStore for getting or setting the location denoted by this previously verified expression in root env.

Parameters:

previously - verified storable expression

Throws:

ThrowException - if completes abruptly with an exception .

getType

public static Class getType(IExpressionNode node,
                            IEnv env)
                     throws VerifyingException

return Class representing Java type of this expression in given env after type checking subexpressions.

Throws:

VerifyingException - if expression is illegal.

isConstant

public static boolean isConstant(IExpressionNode node,
                                 IEnv env)
                          throws VerifyingException

return true if this expression has constant value in given env.

Throws:

VerifyingException - if expression is illegal.

verifyTypes

public static IEnv verifyTypes(IStatementNode node,
                               IEnv env)
                        throws VerifyingException

return IEnv, extended by this statement if it is a local declaration but without evaluating initializers, after verifying types.

Throws:

VerifyingException - if statement is illegal.

eval

public static Object eval(IExpressionNode enode,
                          IEnv env)
                   throws ThrowException

return the value of this previously verified expression in given env.

Throws:

ThrowException - if completes abruptly with an exception

eval

public static IEnv eval(IStatementNode snode,
                        IEnv env)
                 throws AbruptCompletionException

return env extended by this previously verified statement in given env.

Throws:

AbruptCompletionException - if completes abruptly

evalToStore

public static IStore evalToStore(IExpressionStoreNode esnode,
                                 IEnv env)
                          throws ThrowException

return an IStore to get or set the location denoted by this previously verified expression in the given env.

Throws:

ThrowException - if completes abruptly with an exception

shouldNotHappen

public static Error shouldNotHappen(String explain,
                                    Throwable e)

prints stack trace of e on System.err, returns new Error

shouldNotHappen

public static Error shouldNotHappen(Throwable e)

prints stack trace of e on System.err, returns new Error

shouldNotHappen

public static Error shouldNotHappen(String explain)

prints stack trace of thread on System.err, returns new Error