org.erights.e.elang.evm
Class CatchExpr

java.lang.Object
  |
  +--org.erights.e.elang.evm.ParseNode
        |
        +--org.erights.e.elang.evm.ENode
              |
              +--org.erights.e.elang.evm.EExpr
                    |
                    +--org.erights.e.elang.evm.CatchExpr

All Implemented Interfaces:

Cloneable, EPrintable, MatchMaker

public class CatchExpr

extends EExpr

Safe: BNF: "try" block "catch" pattern block.

Evaluates the try-block, but should it throw a Throwable, binds pattern to the Throwable and evaluates the catch-block. The outcome of the catch expression is the outcome of the try-block, or the outcome of the catch-block if the try-block threw a Throwable.

Author:

Mark S. Miller

See Also:

org.erights.e.elang.evm.FinallyExpr, org.erights.e.elang.evm.EscapeExpr

Field Summary

private EExpr	myAttempt
private EExpr	myCatcher
private Pattern	myPattern

Fields inherited from class org.erights.e.elang.evm.ENode

Fields inherited from class org.erights.e.elang.evm.ParseNode

NUM_PR, PR_ASSIGN, PR_CALL, PR_COMP, PR_EEXPR, PR_LISTPATT, PR_ORDER, PR_PATTERN, PR_PRIM, PR_START

Constructor Summary

CatchExpr(SourceSpan optSpan, EExpr attempt, Pattern pattern, EExpr catcher)
Enabled:

Method Summary

EExpr	attempt() Enabled:
protected StaticScope	computeStaticScope() When staticScope() is first requested on a given node, it calls computeStaticScope() to do the actual computation, which is then remembered.
EExpr	katch() Enabled:
boolean	matchBind(ConstList args, Object specimen, FlexList bindings) Enabled:
Pattern	pattern() Enabled:
protected Object	subEval(EvalContext ctx, boolean forValue) Evaluates to the outcome of the try block, but if it throws an Throwable, evaluate to the outcome of the catch block.
void	subPrintOn(TextWriter out, int priority) Enabled:
Object	welcome(ETreeVisitor visitor) Enabled:

Methods inherited from class org.erights.e.elang.evm.EExpr

__printOn, appendAllTo, appendTo, eval, eval, evalBool, printAsBlockOn, substitute, transform

Methods inherited from class org.erights.e.elang.evm.ENode

cleanCopy, copy, getOptPatternMap, getOptScopeMap, getPatternMap, getScopeMap, qbuild, setPatternMap, setScopeMap, staticScope, synEnv

Methods inherited from class org.erights.e.elang.evm.ParseNode

asText, getOptSpan, lnPrintOn, lnPrintOn, matchBind, matchBind, matchBind, printListOn, toString

Methods inherited from class java.lang.Object

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

Field Detail

myAttempt

private final EExpr myAttempt

myPattern

private final Pattern myPattern

myCatcher

private final EExpr myCatcher

Constructor Detail

CatchExpr

public CatchExpr(SourceSpan optSpan,
                 EExpr attempt,
                 Pattern pattern,
                 EExpr catcher)

Enabled:

Method Detail

welcome

public Object welcome(ETreeVisitor visitor)

Enabled:

Specified by:

welcome in class ENode

computeStaticScope

protected StaticScope computeStaticScope()

Description copied from class: ENode

When staticScope() is first requested on a given node, it calls computeStaticScope() to do the actual computation, which is then remembered.

Specified by:

computeStaticScope in class ENode

subEval

protected Object subEval(EvalContext ctx,
                         boolean forValue)

Evaluates to the outcome of the try block, but if it throws an Throwable, evaluate to the outcome of the catch block.

Subtle but important semantic point: Not only do we rethrow the original problem if the catch-pattern fails to match, we also throw the original problem if the match attempt throws, since the original problem is assumed to be a more important diagnostic than the new Throwable.

If the match attempt instead does a non-local escape, then this ejection dominates and the original problem is lost.

Specified by:

subEval in class EExpr

matchBind

public boolean matchBind(ConstList args,
                         Object specimen,
                         FlexList bindings)

Enabled:

Specified by:

matchBind in interface MatchMaker

Specified by:

matchBind in class ParseNode

attempt

public EExpr attempt()

Enabled:

pattern

public Pattern pattern()

Enabled:

katch

public EExpr katch()

Enabled:

subPrintOn

public void subPrintOn(TextWriter out,
                       int priority)
                throws IOException

Enabled:

Specified by:

subPrintOn in class ParseNode

IOException