"

 This is a Manchester Goodie.  It is distributed freely on condition

 that you observe these conditions in respect of the whole Goodie, and on

 any significant part of it which is separately transmitted or stored:

	* You must ensure that every copy includes this notice, and that

	  source and author(s) of the material are acknowledged.

	* These conditions must be imposed on anyone who receives a copy.

	* The material shall not be used for commercial gain without the prior

	  written consent of the author(s).

 For more information about the Manchester Goodies Library (from which 

 this file was distributed) send e-mail:

	To: goodies-lib@cs.man.ac.uk

	Subject: help 

 This is an additional goody-class, which is NOT covered by the

 ST/X license. It has been packaged with the ST/X distribution to

 make your live easier instead. NO WARRANTY.

"

"{ Package: 'stx:libbasic' }"

MetaNumber subclass:#Infinity

	instanceVariableNames:''

	classVariableNames:'InfNeg InfPos'

	poolDictionaries:''

	category:'Magnitude-Numbers'

!

Infinity subclass:#NegativeInfinity

	instanceVariableNames:''

	classVariableNames:''

	poolDictionaries:''

	privateIn:Infinity

!

Infinity subclass:#PositiveInfinity

	instanceVariableNames:''

	classVariableNames:''

	poolDictionaries:''

	privateIn:Infinity

!

Infinity comment:'I have two instances representing positive and negative infinity.

Instance Variables :-

	positive <Boolean>      :       if true the instance represents positive

					infinity. if false, negative infinity'

!

!Infinity class methodsFor:'documentation'!

copyright

"

 This is a Manchester Goodie.  It is distributed freely on condition

 that you observe these conditions in respect of the whole Goodie, and on

 any significant part of it which is separately transmitted or stored:

	* You must ensure that every copy includes this notice, and that

	  source and author(s) of the material are acknowledged.

	* These conditions must be imposed on anyone who receives a copy.

	* The material shall not be used for commercial gain without the prior

	  written consent of the author(s).

 For more information about the Manchester Goodies Library (from which 

 this file was distributed) send e-mail:

	To: goodies-lib@cs.man.ac.uk

	Subject: help 

 This is an additional goody-class, which is NOT covered by the

 ST/X license. It has been packaged with the ST/X distribution to

 make your live easier instead. NO WARRANTY.

"

!

documentation

"

    This is a set of changes that adds infinity in the Number hierarchy.  

    I have two instances representing positive and negative infinity.

    Claus: fixed some minor bugs (args to errorUndefinedResult:) and some wrong comments.

           Changed retry:coercing: to match ST/X's way of doing this

    Instance Variables :-

        positive <Boolean>      :       if true the instance represents positive

                                        infinity. if false, negative infinity

"

!

examples

"

    1 + Infinity positive   

    Infinity positive + 1     

    Infinity positive + Infinity positive     

    Infinity negative - 1                   

    Infinity negative + Infinity negative   

    Infinity negative + Infinity negative   

    Infinity negative negated              

    Infinity positive negated              

    Infinity positive > Infinity negative  

    Infinity negative > Infinity positive  

    Infinity negative + Infinity positive   -> raises an error

    Infinity negative - Infinity negative   -> raises an error

"

!

info

"       

    NAME            infinity

    AUTHOR          manchester

    FUNCTION        Provides a class of infinities

    ST-VERSION      2.2

    PREREQUISITES   

    CONFLICTS

    DISTRIBUTION    world

    VERSION         1

    DATE            22 Jan 1989

    SUMMARY

        This is a set of changes that implements infinity in the Number hierarchy.  

        I obtained the original changes from the author of an article in comp.lang.smalltalk.

        I have just installed it in my image and I have found two small omissions

        which are corrected in what is below; there might be others.  Arithmetic

        between infinities is not defined but magnitude comparisons are implemented.

"

! !

!Infinity class methodsFor:'instance creation'!

negative

    "Return the unique instance of negative infinity"

    ^InfNeg

!

new

    self shouldNotImplement

!

positive

    "Return the unique instance of positive infinity"

    ^InfPos

! !

!Infinity class methodsFor:'class initialization'!

initialize

    InfPos := PositiveInfinity basicNew.

    InfNeg := NegativeInfinity basicNew.

    "

     Infinity initialize

    "

! !

!Infinity methodsFor:'arithmetic'!

* aNumber

    "Multiply the receiver by the argument and answer with the result."

    aNumber isInfinite ifTrue: [

	self errorUndefinedResult: #*.

	^ self class NaN.

    ].

    ^self

!

+ aNumber

    "Add the receiver and the argument and answer with the result."

    (aNumber isInfinite and:[aNumber sign ~~ self sign]) ifTrue: [

	self errorUndefinedResult: #+.

	^ self class NaN

    ].

    ^self

!

- aNumber

    "Subtracet aNumber from the receiver and answer the result."

    (aNumber isInfinite and:[aNumber sign == self sign]) ifTrue: [

        self errorUndefinedResult: #-.

        ^ self class NaN

    ].

    ^self

!

/ aNumber

    "Divide the receiver by the argument and answer the result."

    (aNumber isInfinite or: [aNumber = 0]) ifTrue: [

	self errorUndefinedResult: #/.

	^ self class NaN.

    ].

    ^self

! !

!Infinity methodsFor:'coercing'!

generality

    "Infinities are more general than scalars, but not more general than

     vectors (e.g. Points)"

    ^ 105

!

retryReverseOf: aSymbol with: aNumber

    self obsoleteMethodWarning:'leftover - no longer used'.

    (aSymbol == #* or: [aSymbol == #+]) ifTrue: [

        ^self perform: aSymbol with: aNumber

    ].

    (aSymbol == #/ and: [aNumber isFinite]) ifTrue: [^ 0].

    (aSymbol == #< and: [aNumber isFinite]) ifTrue: [^ self positive].

    (aSymbol == #> and: [ aNumber isFinite ]) ifTrue: [^ self positive not].

    (aSymbol == #= and: [ aNumber isFinite ])ifTrue: [ ^ false ]. 

    self errorUndefinedResult: aSymbol

! !

!Infinity methodsFor:'comparing'!

< aNumber

    "Positive infinity is greater than any number other than positive infinity.

     Analogously, negative infinity is less than any other number other

     than negative infinity"

    aNumber == self ifTrue: [^false].

    ^ self positive not

    "

     Infinity positive < 0              

     Infinity positive < 1000           

     Infinity positive < -1000          

     Infinity positive < Infinity positive 

     Infinity positive < Infinity negative 

     0 < Infinity positive                 

     1000 < Infinity positive              

     -1000 < Infinity positive             

     Infinity negative < Infinity positive 

     Infinity negative < 0                     

     Infinity negative < 1000                  

     Infinity negative < -1000                 

     Infinity negative < Infinity negative     

     Infinity negative < Infinity positive     

     0 < Infinity negative                     

     1000 < Infinity negative                  

     -1000 < Infinity negative                 

     Infinity negative < Infinity positive     

    "

!

= aNumber

    "return true, if the argument represents the same numeric value

     as the receiver, false otherwise."

    aNumber == self ifTrue:[^ true].

    "could be another infinity..."

    aNumber isFinite ifTrue:[^ false].

    ^ aNumber sign == self sign

!

> aNumber

    "Positive infinity is greater than any number other than positive infinity.

     Analogously, negative infinity is less than any other number other

     than negative infinity"

    aNumber == self ifTrue: [^false].

    ^ self positive

    "

     Infinity positive > 0                     

     Infinity positive > 1000                  

     Infinity positive > -1000                 

     Infinity positive > Infinity positive     

     Infinity positive > Infinity negative     

     0 > Infinity positive                     

     1000 > Infinity positive                  

     -1000 > Infinity positive                 

     Infinity negative > Infinity positive     

     Infinity negative > 0                     

     Infinity negative > 1000                  

     Infinity negative > -1000                 

     Infinity negative > Infinity negative     

     Infinity negative > Infinity positive     

     0 > Infinity negative                     

     1000 > Infinity negative                  

     -1000 > Infinity negative                 

     Infinity negative > Infinity positive     

    "

! !

!Infinity methodsFor:'double dispatching'!

differenceFromSomeNumber:aNumber

    "Sent from aNumber-self, if aNumber does not know how to handle this"

    ^ self negated

!

lessFromSomeNumber:aNumber

    "Sent from aNumber < self, if aNumber does not know how to handle this"

    aNumber isFinite ifTrue:[

        ^ self positive.

    ].

    ^ Number

        raise: #undefinedResultSignal

        receiver: self

        selector: #lessFromSomeNumber:

        errorString: 'Cannot compare against NaN'

!

productFromSomeNumber:aNumber

    "Sent from aNumber*self, if aNumber does not know how to handle this"

    aNumber sign >= 0 ifTrue:[

        ^ self

    ].

    ^ self negated

!

quotientFromSomeNumber:aNumber

    "Return the quotient of the argument, aNumber and the receiver.

     Sent when aNumber does not know how to divide by the receiver."

    aNumber sign > 0 ifTrue:[

	^ self

    ].

    aNumber sign < 0 ifTrue:[

	^ self negated

    ].

    ^ aNumber realNumber

!

sumFromSomeNumber:aNumber

    "Sent from aNumber+self, if aNumber does not know how to handle this"

    ^ self

! !

!Infinity methodsFor:'errors'!

errorUndefinedResult: messageName

    ^ Number

	raise: #undefinedResultSignal

	receiver: self

	selector: #lessFromSomeNumber:

	errorString: 'Undefined result in an Infinity ', messageName

! !

!Infinity methodsFor:'testing'!

isFinite

    ^false

!

isInfinite

    ^true

! !

!Infinity::NegativeInfinity methodsFor:'arithmetic'!

negated

    ^ InfPos

!

negative

    ^ true

! !

!Infinity::NegativeInfinity methodsFor:'printing'!

printOn: aStream

    aStream nextPutAll:'-INF'

! !

!Infinity::NegativeInfinity methodsFor:'testing'!

sign

    "return the sign of the receiver (1)"

    ^ -1

! !

!Infinity::PositiveInfinity methodsFor:'arithmetic'!

negated

    ^ InfNeg

!

negative

    ^ false

! !

!Infinity::PositiveInfinity methodsFor:'printing'!

printOn: aStream

    aStream nextPutAll:'INF'

! !

!Infinity::PositiveInfinity methodsFor:'testing'!

sign

    "return the sign of the receiver (-1)"

    ^ 1

! !

!Infinity class methodsFor:'documentation'!

version

! !

Infinity initialize!