What does reduce: get used for?
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I'm not completely following what its purpose is? Below is the code
from the Magritte, living in the SequenceableCollection object: reduce: aBlock | result | self isEmpty ifTrue: [ ^ nil ]. result := self first. 2 to: self size do: [ :index | result := aBlock value: result value: (self at: index) ]. ^ result In my case, it is causing problems on VW when it calls aBlock (near the end) and passes in a pair of Characters which are processed by MAComponentRenderer>>classFor: which then tries to do a string append (#,) which gives a DNU since VW's characters (and I think Squeak from what I can tell) do not have concat methods (#,).. Am I missing something? Below is the code that calls reduce: MAComponentRenderer>>classFor: aDescription | classes item | item := (component description = aDescription ifTrue: [ component ] ifFalse: [ self childAt: aDescription ]) ifNotNilDo: [ :comp | comp model ]. classes := aDescription cssClassesForItem: item. (self hasError: aDescription) ifTrue: [ classes add: 'error' ]. ^ classes reduce: [ :a :b | a , ' ' , b ] _______________________________________________ SmallWiki, Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
Re: What does reduce: get used for?
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> I'm not completely following what its purpose is?
It is a left-fold: http://en.wikipedia.org/wiki/Fold_(higher-order_function) > In my case, it is causing problems on VW when it calls aBlock (near > the end) and passes in a pair of Characters which are processed by > MAComponentRenderer>>classFor: which then tries to do a string append > (#,) which gives a DNU since VW's characters (and I think Squeak from > what I can tell) do not have concat methods (#,).. Am I missing > something? The idea is that when you do #( 'foo' 'bar' 'zork' ) reduce: [ :a :b | a , ' ' , b ] you get 'foo bar zork' I don't know how your collection 'classes' ends up with characters? These should be strings. Maybe there is a bug in #cssClassesForItem:? I don't have such a method in Squeak though and the original implementation of #classFor: looks quite different: MAComponentRenderer>>classFor: aDescription | classes | classes := OrderedCollection withAll: aDescription cssClasses. aDescription isReadonly ifTrue: [ classes add: 'readonly' ]. aDescription isRequired ifTrue: [ classes add: 'required' ]. (self hasError: aDescription) ifTrue: [ classes add: 'error' ]. ^ classes reduce: [ :a :b | a , ' ' , b ] Cheers, Lukas -- Lukas Renggli http://www.lukas-renggli.ch _______________________________________________ SmallWiki, Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
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Lukas Renggli wrote:
>> I'm not completely following what its purpose is? >> > > It is a left-fold: > > http://en.wikipedia.org/wiki/Fold_(higher-order_function) > > >> In my case, it is causing problems on VW when it calls aBlock (near >> the end) and passes in a pair of Characters which are processed by >> MAComponentRenderer>>classFor: which then tries to do a string append >> (#,) which gives a DNU since VW's characters (and I think Squeak from >> what I can tell) do not have concat methods (#,).. Am I missing >> something? >> > > The idea is that when you do > > #( 'foo' 'bar' 'zork' ) reduce: [ :a :b | a , ' ' , b ] > > you get > > 'foo bar zork' > > I don't know how your collection 'classes' ends up with characters? > These should be strings. Maybe there is a bug in #cssClassesForItem:? > > I don't have such a method in Squeak though and the original > implementation of #classFor: looks quite different: > > MAComponentRenderer>>classFor: aDescription > | classes | > classes := OrderedCollection withAll: aDescription cssClasses. > aDescription isReadonly > ifTrue: [ classes add: 'readonly' ]. > aDescription isRequired > ifTrue: [ classes add: 'required' ]. > (self hasError: aDescription) > ifTrue: [ classes add: 'error' ]. > ^ classes reduce: [ :a :b | a , ' ' , b ] > > Cheers, > Lukas > > an Array/Collection of strings is expected. Keith _______________________________________________ SmallWiki, Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
Re: What does reduce: get used for?
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Thanks Keith & Lukas.. Keith was right.. I was passing in a string
instead of an array of strings.. Oh well.. Live and learn.. It's working MUCH better now! -- Rick On Aug 18, 2008, at 8:28 AM, Keith Hodges wrote: > Lukas Renggli wrote: >>> I'm not completely following what its purpose is? >>> >> >> It is a left-fold: >> >> http://en.wikipedia.org/wiki/Fold_(higher-order_function) >> >> >>> In my case, it is causing problems on VW when it calls aBlock (near >>> the end) and passes in a pair of Characters which are processed by >>> MAComponentRenderer>>classFor: which then tries to do a string >>> append >>> (#,) which gives a DNU since VW's characters (and I think Squeak >>> from >>> what I can tell) do not have concat methods (#,).. Am I missing >>> something? >>> >> >> The idea is that when you do >> >> #( 'foo' 'bar' 'zork' ) reduce: [ :a :b | a , ' ' , b ] >> >> you get >> >> 'foo bar zork' >> >> I don't know how your collection 'classes' ends up with characters? >> These should be strings. Maybe there is a bug in #cssClassesForItem:? >> >> I don't have such a method in Squeak though and the original >> implementation of #classFor: looks quite different: >> >> MAComponentRenderer>>classFor: aDescription >> | classes | >> classes := OrderedCollection withAll: aDescription cssClasses. >> aDescription isReadonly >> ifTrue: [ classes add: 'readonly' ]. >> aDescription isRequired >> ifTrue: [ classes add: 'required' ]. >> (self hasError: aDescription) >> ifTrue: [ classes add: 'error' ]. >> ^ classes reduce: [ :a :b | a , ' ' , b ] >> >> Cheers, >> Lukas >> >> > If looks like you have put a string into the cssClasses property, > where > an Array/Collection of strings is expected. > > Keith > > > _______________________________________________ > SmallWiki, Magritte, Pier and Related Tools ... > https://www.iam.unibe.ch/mailman/listinfo/smallwiki > _______________________________________________ SmallWiki, Magritte, Pier and Related Tools ... https://www.iam.unibe.ch/mailman/listinfo/smallwiki |
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