Re: defrecord and overriding "empty"
In core.logic we have a protocol called IUninitialized that you can implement. That works well enough for our needs. On Saturday, December 15, 2012, Joseph Smith wrote: > Well here I am over a year later with the same problem. I'm curious, what > was your solution for the time being? > > On Tuesday, September 27, 2011 1:06:37 PM UTC-5, David Nolen wrote: >> >> On Tue, Sep 27, 2011 at 1:54 PM, Nathan Sorenson wrote: >> >>> Should IPersistentCollection even be defining 'empty', if one of the >>> language's key data types doesn't support it? I think it would be better to >>> either pull 'empty' into it's own protocol so clojure.walk doesn't match on >>> IPersistentCollection when walking a data structure with the false >>> expectation that it can create an empty version, or rename 'empty' it to >>> something that records can implement, like 'default.' >> >> >> This is a fair point. ClojureScript fixes this by providing >> IEmptyableCollection. >> >> David >> > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to > clojure@googlegroups.com 'clojure@googlegroups.com');> > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+unsubscr...@googlegroups.com 'clojure%2bunsubscr...@googlegroups.com');> > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: defrecord and overriding "empty"
Well here I am over a year later with the same problem. I'm curious, what was your solution for the time being? On Tuesday, September 27, 2011 1:06:37 PM UTC-5, David Nolen wrote: > > On Tue, Sep 27, 2011 at 1:54 PM, Nathan Sorenson > > wrote: > >> Should IPersistentCollection even be defining 'empty', if one of the >> language's key data types doesn't support it? I think it would be better to >> either pull 'empty' into it's own protocol so clojure.walk doesn't match on >> IPersistentCollection when walking a data structure with the false >> expectation that it can create an empty version, or rename 'empty' it to >> something that records can implement, like 'default.' > > > This is a fair point. ClojureScript fixes this by providing > IEmptyableCollection. > > David > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: defrecord and overriding "empty"
On Tue, Sep 27, 2011 at 1:54 PM, Nathan Sorenson wrote: > Should IPersistentCollection even be defining 'empty', if one of the > language's key data types doesn't support it? I think it would be better to > either pull 'empty' into it's own protocol so clojure.walk doesn't match on > IPersistentCollection when walking a data structure with the false > expectation that it can create an empty version, or rename 'empty' it to > something that records can implement, like 'default.' This is a fair point. ClojureScript fixes this by providing IEmptyableCollection. David -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: defrecord and overriding "empty"
You're right that my use isn't strictly returning a collection with a size of zero-- I'm treating empty more like 'default'. I'm thinking of its use in clojure.walk, which simply creates a "blank" version of an arbitrary collection in which to place the altered sub-forms. I can't find any other usages of 'empty' in the std lib. I agree it's a bit of a mismatch, as 'walk' won't be able to alter the built-in keys of a record, but you wouldn't expect that to happen if you were using records. Should IPersistentCollection even be defining 'empty', if one of the language's key data types doesn't support it? I think it would be better to either pull 'empty' into it's own protocol so clojure.walk doesn't match on IPersistentCollection when walking a data structure with the false expectation that it can create an empty version, or rename 'empty' it to something that records can implement, like 'default.' -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
Re: defrecord and overriding "empty"
The problem is what does empty mean in the context of defrecord? A new instance of a defrecord is not "empty", it has those fields and they are set to nil. David On Tue, Sep 27, 2011 at 3:48 AM, Nathan Sorenson wrote: > I'm using clojure.walk/postwalk to rewrite terms in nested data > structures. However, I am unable to do this with types as defined by > defrecord, because they specify that the function "empty" throw a not- > implemented exception. > > If I were able to over-ride this default implementation of 'empty' I > believe I could still use postwalk to rewrite my custom records (as > they happily implement 'into' which works as expected.) > > This was my obvious first attempt: > > (defrecord TypeVar [guid name] > clojure.lang.IPersistentCollection > (empty [coll] (TypeVar. 0 nil))) > > Which fails due to: > > "Duplicate method name&signature in class file types/TypeVar" > [Thrown class java.lang.ClassFormatError] > > I would prefer not to fall back on deftype as I do wish these objects > to behave as maps. I also could write my own version of postwalk that > doesn't call 'empty' on my custom-defined records, but it would be > nice to make my types adhere to the contract of IPersistentCollection > as much as possible. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
