edu.mit.ai.psg.jeva
Class EvalMethods

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

public class EvalMethods

extends Object

Centralized static methods for evaluating nodes while catching exceptions. Top level: EvalMethods.evaluate(node, env) verifies types 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 was being evaluated at the time. Similarly, nodes call EvalMethods.getType(expressionNode, env) and EvalMethods.verifyTypes(statementNode, env) 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 stateemnt.
  • ContinueException: evaluated node executed a continue stateemnt.
• VerifyingException: subclasses for non-continueable problems
  • IllegalTypeException: an incompatible type was encountered --- a "compile-time error" in Java Language Specificiation 1.0.
  • IllegalNameException: a missing, ambiguous, or conflicting name was encountered --- a "compile-time error" in Java Language Specificiation 1.0.
  • IllegalConstructException: a Java construct was improperly formed, or used in an improper context --- a "compile-time error" in Java Language Specificiation 1.0.
• EvaluatingError: An error during evaluation, due to a bug.
• VerifyingError: An error during type verification, due to a bug.

Calls evalHook before and after each construct is evaluated. See edu.mit.ai.psg.jeva.examples for examples of using evalHook for tracing.

Author:

CarlManning, caroma@ai.mit.edu
Copyright (c) 1997, 1998, 1999 Massachusetts Institute of Technology

See Also:

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

Inner Class Summary

static class	EvalMethods.AbruptData EvalHook data with AbruptCompletionException (includes ReturnException, ThrowException, BreakException, ContinueException)
static class	EvalMethods.EvalHookData EvalHook is passed instance of EvalHookData: .
static interface	EvalMethods.EvalHookError
static class	EvalMethods.EvalHookPostData
static class	EvalMethods.EvalHookPreData
static class	EvalMethods.PreEvalData EvalHook data prior to evaluating expression or statement
static class	EvalMethods.PreEvalToStoreData EvalHook data prior to evaluating expression to store target for assignment
static class	EvalMethods.ResultData EvalHook data with expression result value
static class	EvalMethods.ResultEnvData EvalHook data with statement result environment
static class	EvalMethods.ResultStoreData EvalHook data with expression store target for assignment

Field Summary

static IEnv	defaultEnv
static IJevaVisitor	evalHook if EvalHook is non null, it is called before and after each node is evaluated, with the appropriate EvalMethods#EvalHookData.

Method Summary

static Object	eval(IExpressionNode node)
static Object	eval(IExpressionNode enode, IEnv env)
static IEnv	eval(IStatementNode node)
static IEnv	eval(IStatementNode snode, IEnv env)
static void	eval(JNCompilationUnit node, String[] arguments) Finds public class of previously verified compilation unit, runs public static void main(String[]) method of this public class if one exists.
static void	eval(JNCompilationUnit node, String[] arguments, IEnv env) Calls "public static void main(String[])" method of public class in compilation unit.
static IStore	evalToStore(IExpressionStoreNode node)
static IStore	evalToStore(IExpressionStoreNode esnode, IEnv 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 void	evaluate(JNCompilationUnit node, String[] arguments) verify types with default env, then find class with public static void main(String[]) method and call it with arguments.
static void	evaluate(JNCompilationUnit node, String[] arguments, IEnv env) verify types with env, then find public class with public static void main(String[]) method and call it with arguments.
static IClass	getType(IExpressionNode node)
static IClass	getType(IExpressionNode node, IEnv env)
static boolean	isConstant(IExpressionNode node)
static boolean	isConstant(IExpressionNode node, IEnv env)
static IEnv	verifyTypes(IStatementNode node)
static IEnv	verifyTypes(IStatementNode node, IEnv env)
static IEnv	verifyTypes(JNCompilationUnit node)
static IEnv	verifyTypes(JNCompilationUnit node, IEnv env) Scans compilation unit for class declarations, computes type signatures of methods, and verifies types in fields and methods.

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

evalHook

public static IJevaVisitor evalHook

if EvalHook is non null, it is called before and after each node is evaluated, with the appropriate EvalMethods#EvalHookData. See edu.mit.ai.psg.jeva.examples for examples using evalHook for tracing.

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:

default env possibly extended by statement (e.g,. if local decl)

Throws:

VerifyingException - if statement is illegal

AbruptCompletionException - if completes abruptly

evaluate

public static void evaluate(JNCompilationUnit node,
                            String[] arguments)
                     throws VerifyingException,
                            ClassNotFoundException,
                            ThrowException

verify types with default env, then find class with public static void main(String[]) method and call it with arguments.

Throws:

VerifyingException - if compilation unit is illegal

ClassNotFoundException - if no public class with main method found.

ThrowException - if call completes with an exception

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

evaluate

public static void evaluate(JNCompilationUnit node,
                            String[] arguments,
                            IEnv env)
                     throws VerifyingException,
                            ClassNotFoundException,
                            ThrowException

verify types with env, then find public class with public static void main(String[]) method and call it with arguments.

Throws:

VerifyingException - if compilation unit is illegal

ClassNotFoundException - if no public class with main found

ThrowException - if call completes with an exception

getType

public static IClass getType(IExpressionNode node)
                      throws VerifyingException

Returns:

the IClass 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

Returns:

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:

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

Throws:

VerifyingException - if statement is illegal.

verifyTypes

public static IEnv verifyTypes(JNCompilationUnit node)
                        throws VerifyingException

Returns:

defaultEnv, as modified by this compilation unit after verifying its types, but without evaluating initializers.

Throws:

VerifyingException - if compilation unit is illegal.

eval

public static Object eval(IExpressionNode node)
                   throws ThrowException

Parameters:

node - previously verified expression

Returns:

the value of expression in root env.

Throws:

ThrowException - if completes abruptly with an exception

eval

public static IEnv eval(IStatementNode node)
                 throws AbruptCompletionException

Parameters:

node - previously verified statement

Returns:

IEnv, extended by statement if it is a local declaration.

Throws:

AbruptCompletionException - if completes abruptly

eval

public static void eval(JNCompilationUnit node,
                        String[] arguments)
                 throws ClassNotFoundException,
                        ThrowException

Finds public class of previously verified compilation unit, runs public static void main(String[]) method of this public class if one exists.

Parameters:

node - previously verified compilation unit

Returns:

IEnv, as modified by this compilation unit.

Throws:

ClassNotFoundException - if no public class with main found.

ThrowException - if completes abruptly with an exception

evalToStore

public static IStore evalToStore(IExpressionStoreNode node)
                          throws ThrowException

Parameters:

node - previously verified storable expression

Returns:

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

Throws:

ThrowException - if completes abruptly with an exception .

getType

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

Returns:

IClass 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

Returns:

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

Returns:

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

Throws:

VerifyingException - if expression is illegal.

verifyTypes

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

Scans compilation unit for class declarations, computes type signatures of methods, and verifies types in fields and methods. (If processing many units, it may be better to scan all, then compute all, then verify all, to reduce file system searching for names.)

Returns:

env; no additions are visible outside compilation unit.

Throws:

VerifyingException - if expression is illegal.

eval

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

Returns:

the value of this expression in given env.

Throws:

ThrowException - if completes abruptly with an exception

evalToStore

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

Returns:

an IStore to get or set the location denoted by this expression.

Throws:

ThrowException - if completes abruptly with an exception

eval

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

Returns:

env possibly extended by this statement in given env.

Throws:

AbruptCompletionException - if completes abruptly

eval

public static void eval(JNCompilationUnit node,
                        String[] arguments,
                        IEnv env)
                 throws ThrowException,
                        ClassNotFoundException

Calls "public static void main(String[])" method of public class in compilation unit.

Throws:

ClassNotFoundException - if no public class with main method found.

ThrowException - if completes abruptly with an exception