Compiler.LogicalData (P2J - Progress 4GL to Java Conversion and Runtime)

java.lang.Object
- com.goldencode.expr.Compiler.LogicalData

Enclosing class:

Compiler
```
private static class Compiler.LogicalData
extends java.lang.Object
```
Helper class which stores information to assist when assembling branch instructions for logical tests. Instances of this class are attached to nodes in the expression's AST during the compiler's preprocessing step. When these nodes (which represent logical tests which must evaluate to true or false) are assembled into bytecode instructions, this object is consulted to determine whether the flow of control should proceed normally to the next instruction, or whether it should branch to another instruction, effectively bypassing sets of instructions made irrelevant at runtime.
An instance of this class defines a trueTarget, which is the AST which logically represents the destination instruction in the event the underlying logical test evaluates to true. It also defines a falseTarget, which is the AST which logically represents the destination instruction in the event the underlying test evaluates to false. Since branching instructions which test a condition only allow a jump in one case or the other (otherwise execution proceeds normally to the next instruction in the bytecode array), only one target can be active. The active target is defined by the trigger flag. The preprocess step of compilation does the hard work of determining how to apply instances of this class to AST nodes appropriately, based upon some basic rules of boolean algebra.
An extra field exists to hold the data previously stored in the extra field of the associated AST. This is necessary because we usurp that field in the AST to store an instance of this class, but we do not want to lose the original data, which is still needed after preprocessing the expression AST.
Finally, this class defines a topOfBranch flag, which is used to denote that the associated AST represents the highest level logical operation in a chain. This may be the root of the entire expression, or it may be the base of an AST branch which resolves to a boolean value, but whose parent is not a logical operator (for example, the parent could represent a method call which accepts a boolean argument, but does not have a boolean return type). In either case the topOfBranch designation is used to determine that an additional pair of instructions is necessary as the targets of the top level AST: one that pushes a true result onto the runtime stack, and one that pushes a false result onto the stack. These then become the targets of the top level, logical operation, since no other natural jump target exists.

See Also:

Compiler.preprocess(com.goldencode.expr.ExtraAst), Compiler.assemble(com.goldencode.expr.ExtraAst), CodeUnit.BranchData

Field Summary

Fields
Modifier and Type	Field and Description
`private java.lang.Object`	`extra` Data object originally stored in the extra field of an AST
`private ExtraAst`	`falseTarget` AST which defines the destination instruction for a false result
`private boolean`	`topOfBranch` Flag indicating AST represents top of chain of logical operations
`private boolean`	`trigger` Logical test result which will trigger a jump
`private ExtraAst`	`trueTarget` AST which defines the destination instruction for a true result

Constructor Summary

Constructors
Constructor and Description
`LogicalData(boolean trigger, java.lang.Object extra)` Constructor which defines this object's trigger condition and stores the "extra" data previously stored in this object's new host AST.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`(package private) java.lang.Object`	`getExtra()` Get the "extra" data previously associated with the underlying AST.
`(package private) ExtraAst`	`getFalseTarget()` Get the AST which represents this object's logical destination if a `false` result is achieved.
`(package private) ExtraAst`	`getTarget()` Get the AST which represents the target to which the underlying AST's compiled code will jump when the trigger result is produced.
`(package private) boolean`	`getTrigger()` Get the trigger condition for this object.
`(package private) ExtraAst`	`getTrueTarget()` Get the AST which represents this object's logical destination if a `true` result is achieved.
`(package private) boolean`	`isTopOfBranch()` Report whether the underlying AST represents the base of a branch of logical operations.
`(package private) void`	`setFalseTarget(ExtraAst falseTarget)` Set the AST which represents this object's logical destination if a `false` result is achieved.
`(package private) void`	`setTopOfBranch(boolean topOfBranch)` Set whether the underlying AST represents the base of a branch of logical operations.
`(package private) void`	`setTrueTarget(ExtraAst trueTarget)` Set the AST which represents this object's logical destination if a `true` result is achieved.
`java.lang.String`	`toString()` Generate a string representation of this object for debugging purposes.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - trueTarget
```
private ExtraAst trueTarget
```
    AST which defines the destination instruction for a true result
  - falseTarget
```
private ExtraAst falseTarget
```
    AST which defines the destination instruction for a false result
  - extra
```
private java.lang.Object extra
```
    Data object originally stored in the extra field of an AST
  - trigger
```
private boolean trigger
```
    Logical test result which will trigger a jump
  - topOfBranch
```
private boolean topOfBranch
```
    Flag indicating AST represents top of chain of logical operations
- Constructor Detail
  - LogicalData
```
LogicalData(boolean trigger,
            java.lang.Object extra)
```
    Constructor which defines this object's trigger condition and stores the "extra" data previously stored in this object's new host AST.
    
    Parameters:
    
    trigger - true to jump to trueTarget on a true result; false to jump to falseTarget on a false result.
    
    extra - "Extra" data previously stored in this object's new host AST.
- Method Detail
  - getTrigger
```
boolean getTrigger()
```
    Get the trigger condition for this object.
    
    Returns:
    
    true if we jump on true; false if we jump on false.
  - isTopOfBranch
```
boolean isTopOfBranch()
```
    Report whether the underlying AST represents the base of a branch of logical operations.
    
    Returns:
    
    true if AST is such a node, else false.
  - setTopOfBranch
```
void setTopOfBranch(boolean topOfBranch)
```
    Set whether the underlying AST represents the base of a branch of logical operations.
    
    Parameters:
    
    topOfBranch - true if AST is such a node, else false.
  - getExtra
```
java.lang.Object getExtra()
```
    Get the "extra" data previously associated with the underlying AST.
    
    Returns:
    
    AST's original "extra" object.
  - getTarget
```
ExtraAst getTarget()
```
    Get the AST which represents the target to which the underlying AST's compiled code will jump when the trigger result is produced. A jump will only trigger on one result, true or false. The opposite result will cause execution to proceed normally to the next instruction in the bytecode array instead of causing a jump.
    
    Returns:
    
    The trueTarget defined for this object if its trigger is true; else its falseTarget.
  - getTrueTarget
```
ExtraAst getTrueTarget()
```
    Get the AST which represents this object's logical destination if a true result is achieved. This transition represents a branch only if trigger is true; otherwise it represents normal, contiguous execution.
    
    Returns:
    
    Target AST for a true result.
  - setTrueTarget
```
void setTrueTarget(ExtraAst trueTarget)
```
    Set the AST which represents this object's logical destination if a true result is achieved.
    
    Parameters:
    
    trueTarget - Target AST for a true result.
  - getFalseTarget
```
ExtraAst getFalseTarget()
```
    Get the AST which represents this object's logical destination if a false result is achieved. This transition represents a branch only if trigger is false; otherwise it represents normal, contiguous execution.
    
    Returns:
    
    Target AST for a false result.
  - setFalseTarget
```
void setFalseTarget(ExtraAst falseTarget)
```
    Set the AST which represents this object's logical destination if a false result is achieved.
    
    Parameters:
    
    falseTarget - Target AST for a false result.
  - toString
```
public java.lang.String toString()
```
    Generate a string representation of this object for debugging purposes.
    
    Overrides:
    
    toString in class java.lang.Object
    
    Returns:
    
    String representing this object's internal state.

Class Compiler.LogicalData

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

trueTarget

falseTarget

extra

trigger

topOfBranch

Constructor Detail

LogicalData

Method Detail

getTrigger

isTopOfBranch

setTopOfBranch

getExtra

getTarget

getTrueTarget

setTrueTarget

getFalseTarget

setFalseTarget

toString