org.erights.e.elang.evm
Class DefineExpr

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.DefineExpr

All Implemented Interfaces:

Cloneable, EPrintable, MatchMaker

public class DefineExpr

extends EExpr

Safe: BNF: "def" pattern ":=" eExpr

Introduce a binding for 'pattern' in the nearest layer of the current environment. 'pattern' must not yet have a binding in this layer.

For a DefineExpr to be well formed, none of the variables defined by pattern (ie, pattern.staticScope().outNames()) may be used by eExpr (ie, eExpr.staticScope().namesUsed()), and vice versa. By imposing this restriction in the kernel language, the kernel language may evaluate these two in the wrong order (right to left) without violating the left to right scoping rule. Therefore, the kernel language remains a valid subset of the user language, in that all kernel programs are valid user programs with the same meaning. A user-level def-expression that violates the above rules is expanded into a kernel-level one that satisfies it.

Author:

Mark S. Miller

Field Summary

private Pattern	myPattern
private EExpr	myRValue

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

DefineExpr(SourceSpan optSpan, Pattern pattern, EExpr rValue)
Enabled: If the resulting DefineExpr isn't well formed (see class comment), this throws a (XXX to be defined) exception.

Method Summary

protected StaticScope	computeStaticScope() When staticScope() is first requested on a given node, it calls computeStaticScope() to do the actual computation, which is then remembered.
private void	ensureWellFormed()
boolean	matchBind(ConstList args, Object specimen, FlexList bindings) Enabled:
Pattern	pattern() Enabled:
EExpr	rValue() Enabled:
protected Object	subEval(EvalContext ctx, boolean forValue) The recursive part that does the work
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

myPattern

private final Pattern myPattern

myRValue

private final EExpr myRValue

Constructor Detail

DefineExpr

public DefineExpr(SourceSpan optSpan,
                  Pattern pattern,
                  EExpr rValue)

Enabled: If the resulting DefineExpr isn't well formed (see class comment), this throws a (XXX to be defined) exception.

Method Detail

ensureWellFormed

private void ensureWellFormed()

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)

Description copied from class: EExpr

The recursive part that does the work

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

pattern

public Pattern pattern()

Enabled:

subPrintOn

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

Enabled:

Specified by:

subPrintOn in class ParseNode

IOException

rValue

public EExpr rValue()

Enabled: