Class: False

• Inheritance
• Description
• Instance protocol
  • Javascript support
  • conditional evaluation
  • converting
  • debugging
  • inspecting
  • logical operations
  • printing & storing

Inheritance:

   Object
   |
   +--Boolean
      |
      +--False

Package:

stx:libbasic

Category:

Kernel-Objects

Version:

rev: 1.39 date: 2022/03/16 13:28:44

user: stefan

file: False.st directory: libbasic

module: stx stc-classLibrary: libbasic

Description:

False has only one instance, false, representing logical falsehood.

Some methods are implemented here and in True, instead of the common
superclass Boolean. This has the advantage that no truth-value checks
are needed, but instead the truth check is done in the method lookup.
However, remember that some messages to booleans are inline coded in
the compilers (both interpreted and machine code). Therefore redefinition
of some methods here will not have any effect on compiled code.
(redefining ifTrue: to something else will probably crash the smalltalk
 world anyway ...)

copyright
COPYRIGHT (c) 1988 by Claus Gittinger
             All Rights Reserved

This software is furnished under a license and may be used
only in accordance with the terms of that license and with the
inclusion of the above copyright notice.   This software may not
be provided or otherwise made available to, or used by, any
other person.  No title to or ownership of the software is
hereby transferred.

Instance protocol:

 js_not
( an extension from the stx:libjavascript package )

 and: aBlock

evaluate aBlock if the receiver is true.
(since the receiver is known to be false here, always return false here).
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2

evaluate block1 if the receiver is true; if that also returns true, evaluate block2.
(since the receiver is known to be false here, always return false here).
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2 and: block3

evaluate block1 if the receiver is true;
if that also returns true, evaluate block2;
if that also returns true, evaluate block3.
(since the receiver is known to be false here, always return false here).
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 and: block1 and: block2 and: block3 and: block4

evaluate block1 if the receiver is true;
if that also returns true, evaluate block2;
if that also returns true, evaluate block3.
if that also returns true, evaluate block4.
(since the receiver is known to be false here, always return false here).
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifFalse: aBlock

If the receiver is false, return the value of evaluating aBlock; nil otherwise.
Since the receiver is definitely false here, unconditionally return the block's value.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifFalse: falseBlock ifTrue: trueBlock

return the value of evaluating falseBlock (since the receiver is false)
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifTrue: aBlock

If the receiver is true, return the value of evaluating aBlock; nil otherwise.
Since the receiver is definitely false here, unconditionally return nil value.
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 ifTrue: trueBlock ifFalse: falseBlock

return the value of evaluating falseBlock (since the receiver is false)
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: aBlock

evaluate aBlock if the receiver is false.
(since the receiver is false return the value of evaluating aBlock).
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2

evaluate block1 if the receiver is false.
if that evaluates to false, return the result from block2.
(since the receiver is false return the value of evaluating aBlock).
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2 or: block3

evaluate block1 if the receiver is false.
if that evaluates to false, return the result from block2.
if that evaluates to false, return the result from block3.
(since the receiver is false return the value of evaluating aBlock).
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 or: block1 or: block2 or: block3 or: block4

evaluate block1 if the receiver is false.
if that evaluates to false, return the result from block2.
if that evaluates to false, return the result from block3.
if that evaluates to false, return the result from block4.
(since the receiver is false return the value of evaluating aBlock).
Notice:
This method may be open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 asInteger

false->0; true->1

 asNumber

false->0; true->1

 haltIfFalse

halt if the receiver is true

Usage example(s):

3 haltIfNil nil haltIfNil true haltIfTrue true haltIfFalse false haltIfTrue false haltIfFalse

 haltIfTrue

halt if the receiver is true

 inspectorValueListIconFor: anInspector
( an extension from the stx:libtool package )

returns the icon to be shown alongside the value list of an inspector

 & aBoolean

return true, if both the receiver and the argument are true
(since the receiver is false, return false)
Notice:
as this is a binary message, the argument is always evaluated.
It might be better to use and:[...], which does not evaluate
the argument if the receiver is already false.

 ==> aBoolean

same as implies:
return true if receiver implies the argument

 eqv: aBoolean

return true, if the receiver and the argument are the same truth value
(since the receiver is false, return true if the argument is also false)

 implies: aBoolean

return true if receiver ==> argument.
That is: if a is true, b must be true; if a is false, b can be any

 not

return true, if the receiver is false, false otherwise
(since the receiver is false, return true).
Notice:
This method is open coded (inlined) by the compiler(s)
- redefining it may not work as expected.

 xor: aBoolean

return true, if the receiver and the argument are different truth values
(since the receiver is false, return true, if the armument is not false)

 | aBoolean

return true, if either the receiver or the argument is true
(since the receiver is false, return the argument).
Notice:
as this is a binary message, the argument is always evaluated.
It might be better to use or:[...], which does not evaluate
the argument if the receiver is already true.

 printString

return character sequence representing the receiver