Module Simula

Package simula.compiler.syntaxClass.expression

Class BooleanExpression

java.lang.Object

simula.compiler.syntaxClass.SyntaxClass

simula.compiler.syntaxClass.expression.Expression

simula.compiler.syntaxClass.expression.BooleanExpression

public final class BooleanExpression
extends Expression

Boolean expressions

 Simula Standard: 3.2 Boolean expressions

    Boolean-expression
        =  simple-Boolean-expression
        |  IF Boolean-expression THEN  simple-Boolean-expression  ELSE  Boolean-expression

    simple-Boolean-expression
        =  Boolean-tertiary  { OR ELSE  Boolean-tertiary }

    Boolean-tertiary
        =  equivalence  { AND THEN  equivalence }

    equivalence
        =  implication  { EQV  implication }

    implication
        =  Boolean-term  { IMP  Boolean-term }

    Boolean-term
        =  Boolean-factor  { OR  Boolean-factor }

    Boolean-factor
        =  Boolean-secondary  { AND  Boolean-secondary }

    Boolean-secondary
        =  [ NOT ]  Boolean-primary

    Boolean-primary
        =  logical-value
        |  variable
        |  function-designator
        |  relation
        |  "("  Boolean-expression  ")"
 

A Boolean expression is of type Boolean. It is a rule for computing a logical value. Except for the operators and then and or else (see 3.4) the semantics are entirely analogous to those given for arithmetic expressions.

Variables and function designators entered as Boolean primaries must be of type Boolean. Simula Standard: 3.4 The logical operators

The meaning of the logical operators not, and, or, imp, and eqv is given by the following function table:

        b1               false     false     true      true
        b2               false     true      false     true
      ---------------------------------------------------------
        not  b1          true      true      false     false
        b1 and b2        false     false     false     true
        b1 or b2         false     true      true      true
        b1 imp b2        true      true      false     true
        b1 eqv b2        true      false     false     true
     ----------------------------------------------------------
 

The operation "b1 and then b2" denotes "conditional and". If the value of b1 is false the operation yields the result false, otherwise it yields the result of evaluating b2.

The operation "b1 or else b2" denotes "conditional or". If the value of b1 is true the operator yields the result true, otherwise it yields the result of evaluating b2.

Note: The value of "b1 and then b2" is given by textual substitution of the Boolean expression "(if b1 then b2 else false)". Similarly, the operation "b1 or else b2" is defined by substitution of "(if b1 then true else b2)". These definitions imply that the evaluation of the second operand is suppressed when the evaluation result is already evident from the value of the first operand alone.

Link to GitHub: Source File.

Author:

Simula Standard, Øystein Myhre Andersen

Field Summary

Fields

Modifier and Type	Field	Description
private Expression	lhs	The left hand side
private final KeyWord	opr	The Boolean operation
private Expression	rhs	The right hand side

Fields inherited from class simula.compiler.syntaxClass.expression.Expression

backLink, type

Fields inherited from class simula.compiler.syntaxClass.SyntaxClass

lineNumber

Constructor Summary

Constructors

Constructor	Description
BooleanExpression(Expression lhs, KeyWord opr, Expression rhs)	Create a new BooleanExpression.

Method Summary

Modifier and Type	Method	Description
void	doChecking()	Perform semantic checking.
boolean	maybeStatement()	Returns true if this expression may be used as a statement.
String	toJavaCode()	Generate Java code for this Syntax Class.
String	toString()

Methods inherited from class simula.compiler.syntaxClass.expression.Expression

acceptExpression, checkCompatibility, evaluate, expectExpression, get, getInt, getNumber, getQualification, getWriteableVariable, printTree, put

Methods inherited from class simula.compiler.syntaxClass.SyntaxClass

ASSERT_SEMANTICS_CHECKED, doDeclarationCoding, doJavaCoding, edIndent, edTreeIndent, IS_SEMANTICS_CHECKED, print, SET_SEMANTICS_CHECKED

Methods inherited from class java.lang.Object

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

Field Details

lhs

private Expression lhs

The left hand side

opr

private final KeyWord opr

The Boolean operation

rhs

private Expression rhs

The right hand side

Constructor Details

BooleanExpression

BooleanExpression(Expression lhs,
 KeyWord opr,
 Expression rhs)

Create a new BooleanExpression.

Parameters:

lhs - left hand side

opr - Boolean operation

rhs - right hand side

Method Details

doChecking

public void doChecking()

Description copied from class: SyntaxClass

Perform semantic checking.

This must be redefined in every subclass.

Overrides:

doChecking in class SyntaxClass

maybeStatement

public boolean maybeStatement()

Description copied from class: Expression

Returns true if this expression may be used as a statement.

Specified by:

maybeStatement in class Expression

Returns:

true if this expression may be used as a statement

toJavaCode

public String toJavaCode()

Description copied from class: SyntaxClass

Generate Java code for this Syntax Class.

Overrides:

toJavaCode in class SyntaxClass

Returns:

Java code

toString

public String toString()

Overrides:

toString in class Expression