"
COPYRIGHT (c) 1996 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.
"
"{ Package: 'stx:goodies' }"
PeekableStream subclass:#FilteringStream
instanceVariableNames:'inputStream outputStream filter readAhead'
classVariableNames:''
poolDictionaries:''
category:'Streams-Misc'
!
!FilteringStream class methodsFor:'documentation'!
copyright
"
COPYRIGHT (c) 1996 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.
"
!
documentation
"
A FilteringStream can be connected to some input
(from which elements are read via the ReadStream protocol),
and/or to some output (to which elements are written via
the WriteStream protocol.
The FilteringStream itself performs filtering/processing
on the elements as they arrive, optionally suppressing
elements.
A FilteringStream can be operated in pull-mode, by asking
it for the next element; it will then ask its inputStream for
and element, process it and return it.
Or, in pushMode, by having someone else writing elements via
nextPut:; it will then process the element, and send it to its
output stream.
Mixing modes does not make sense, since if pulled, data will not
be written to the outputStream (unless the puller does it).
The connected streams need not be real streams; anything which
responds to the basic Stream protocol can be connected
(a Transcript, a RandomNumber generator or even a Plug will do as well).
[instance variables:]
inputStream <Stream> the stream from which elements are read
outputStream <Stream> the stream to which elements are written
filter <Block> the filter block;
unbound <Boolean> if true, the stream is unbound.
[author:]
Claus Gittinger
[See also:]
ReadStream WriteStream
"
!
examples
"
pushing the contents of a stream onto another stream
(here, the Transcript) without a need to read everything into a
buffer or to reinvent the read-loop:
(notice, a FilteringLineStream does this with less overhead,
due to the byte-wise reading done here)
[exBegin]
|in pusher|
in := 'Makefile' asFilename readStream.
pusher := FilteringStream readingFrom:in writingTo:Transcript.
pusher filterUpToEnd
[exEnd]
filter random numbers:
[exBegin]
|in filter|
in := Random new.
filter := FilteringLineStream readingFrom:in.
filter filter:[:num | ((num >= 0.5) and:[num <= 0.6]) ifTrue:[num] ifFalse:[nil]].
20 timesRepeat:[
Transcript showCR:(filter next printString).
]
[exEnd]
filtering prime numbers:
[exBegin]
|num generator primeFilter addFilter|
num := 1.
generator := Plug new.
generator respondTo:#next
with:[num := num + 1. num].
generator respondTo:#atEnd
with:[false].
addFilter := [:prime | |newFilter|
newFilter := FilteringStream basicNew.
newFilter filter:[:num | (num \\ prime) == 0 ifTrue:[
nil
] ifFalse:[
num
]
].
newFilter inputStream:primeFilter.
primeFilter := newFilter
].
addFilter value:2.
primeFilter inputStream:generator.
10000 timesRepeat:[
|nextPrime|
nextPrime := primeFilter next.
addFilter value:nextPrime.
Transcript showCR:nextPrime.
]
[exEnd]
"
! !
!FilteringStream class methodsFor:'instance creation'!
new
"create and return a new filteringStream.
The resulting stream must be connected to some other stream,
before being used"
^ self basicNew initialize.
"Created: 11.1.1997 / 15:31:30 / cg"
"Modified: 11.1.1997 / 15:33:13 / cg"
!
on:something
"create and return a new filteringStream, which reads from
something (which must be convertable to a stream)"
^ self readingFrom:something readStream
"Created: 11.1.1997 / 19:19:34 / cg"
!
readingFrom:aReadStream
"create and return a new filteringStream, which reads from
another stream"
^ (self basicNew inputStream:aReadStream) initialize.
"Created: 11.1.1997 / 15:32:15 / cg"
!
readingFrom:aReadStream writingTo:aWriteStream
"create and return a new filteringStream, which reads from
aReadStream and writes to aWriteStream."
|newStream|
newStream := self basicNew.
newStream inputStream:aReadStream.
newStream outputStream:aWriteStream.
newStream initialize.
^ newStream
"Created: 11.1.1997 / 15:32:28 / cg"
!
writingTo:aWriteStream
"create and return a new filteringStream, which writes to
another stream"
^ (self basicNew outputStream:aWriteStream) initialize.
"Created: 11.1.1997 / 15:32:36 / cg"
! !
!FilteringStream methodsFor:'access - pull-reading'!
contents
^ inputStream contents
!
filterUpToEnd
"pull input from inputStream up to the end,
push it filtered into the outputStream."
[inputStream atEnd] whileFalse:[
self nextPut:(inputStream next)
].
"Created: 2.7.1996 / 21:06:42 / cg"
"Modified: 11.1.1997 / 16:08:35 / cg"
!
next
"pull input from inputStream and
push it filtered into the outputStream"
|input output|
"/ readAhead input has already been filtered
"/ (see #atEnd)
readAhead notNil ifTrue:[
input := readAhead.
readAhead := nil.
^ input
].
[inputStream atEnd] whileFalse:[
"/ get an element
input := inputStream next.
filter isNil ifTrue:[
^ input
].
"/ filter it - this may return nil, to eat it
output := filter value:input.
output notNil ifTrue:[
"/ good - output it
^ output.
].
].
^ nil
"Created: 2.7.1996 / 21:09:58 / cg"
"Modified: 11.1.1997 / 17:17:27 / cg"
!
peek
"peek ahead for the next character"
|input output|
readAhead notNil ifTrue:[
^ readAhead
].
[inputStream atEnd] whileFalse:[
"/ get an element
input := inputStream peek.
filter isNil ifTrue:[
^ input
].
"/ filter it - this may return nil, to eat it
inputStream next.
output := filter value:input.
output notNil ifTrue:[
"/ good - output it
readAhead := output.
^ output.
].
].
^ self pastEndRead
!
peekOrNil
"peek ahead for the next character, or return nil"
|input output|
readAhead notNil ifTrue:[
^ readAhead
].
[inputStream atEnd] whileFalse:[
"/ get an element
input := inputStream peek.
filter isNil ifTrue:[
^ input
].
"/ filter it - this may return nil, to eat it
inputStream next.
output := filter value:input.
output notNil ifTrue:[
"/ good - output it
readAhead := output.
^ output.
].
].
^ nil
! !
!FilteringStream methodsFor:'access - push-writing'!
nextPut:something
"push something through the filter"
|output|
"/ filter it
filter isNil ifTrue:[
outputStream nextPut:something
] ifFalse:[
output := filter value:something.
output notNil ifTrue:[
outputStream nextPut:output
]
]
"Modified: 11.1.1997 / 16:12:52 / cg"
! !
!FilteringStream methodsFor:'accessing'!
filter
"return the filter"
^ filter
"Modified: 2.7.1996 / 21:03:36 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
!
filter:something
"set the filter"
filter := something.
"Modified: 2.7.1996 / 21:03:40 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
!
inputStream
"return the inputStream"
^ inputStream
"Modified: 2.7.1996 / 21:03:43 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
!
inputStream:something
"set the inputStream"
inputStream := something.
"Modified: 2.7.1996 / 21:03:46 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
!
outputStream
"return the outputStream"
^ outputStream
"Modified: 2.7.1996 / 21:03:49 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
!
outputStream:something
"set the outputStream"
outputStream := something.
"Modified: 2.7.1996 / 21:03:52 / cg"
"Created: 2.7.1996 / 21:06:42 / cg"
! !
!FilteringStream methodsFor:'misc'!
close
"when I am closed, close my input - if any"
inputStream notNil ifTrue:[
inputStream close
]
"Created: 11.1.1997 / 15:27:17 / cg"
! !
!FilteringStream methodsFor:'queries'!
atEnd
"return true, if the receiver stream is at the end"
|nextElement|
readAhead notNil ifTrue:[^ false].
filter isNil ifTrue:[
"/ then, its easy
^ inputStream atEnd
].
"/ with a filter, things are more complicated,
"/ since we cannot tell, without asking the filter ...
[inputStream atEnd] whileFalse:[
nextElement := inputStream next.
readAhead := filter value:nextElement.
readAhead notNil ifTrue:[^ false].
].
^ true
"Modified: 11.1.1997 / 17:16:45 / cg"
!
contentsSpecies
"return the kind of collection I should return when asked
for multiple elements."
^ inputStream contentsSpecies
"Created: 11.1.1997 / 16:23:22 / cg"
!
position
"return the receiver streams position"
|rawPosition|
rawPosition := inputStream position.
readAhead notNil ifTrue:[
rawPosition := rawPosition - 1
].
^ rawPosition
!
position0Based
"return the receiver streams position"
|rawPosition|
rawPosition := inputStream position0Based.
readAhead notNil ifTrue:[
rawPosition := rawPosition - 1
].
^ rawPosition
!
position1Based
"return the receiver streams position"
|rawPosition|
rawPosition := inputStream position1Based.
readAhead notNil ifTrue:[
rawPosition := rawPosition - 1
].
^ rawPosition
! !
!FilteringStream class methodsFor:'documentation'!
version
^ '$Header: /cvs/stx/stx/libbasic2/FilteringStream.st,v 1.11 2004-10-01 07:53:42 cg Exp $'
! !