Thanks very much Michael and Jonas. On Monday, 4 March 2013 07:20:24 UTC, Jonas wrote: > > Hi > > You can use the tempid ( > http://docs.datomic.com/clojure/index.html#datomic.api/tempid) function > to generate new temporary ids. > > Jonas > > On Monday, March 4, 2013 8:50:56 AM UTC+2, edw...@kenworthy.info wrote: >> >> Okay, I think I understand that. >> >> Does that mean this code could never work as intended in a Clojure >> program, only at the repl (which seems a bit of a limitation) or is there a >> way to make it work as intended, generating a different id each time? Or is >> the whole approach taken in this code flawed? >> >> On Sunday, 3 March 2013 21:59:45 UTC, Michał Marczyk wrote: >>> >>> #db/id ... is a "tagged literal". It gets read in as an id object with >>> some integer inside. The way this happens is that the reader looks up >>> a "data reader" function associated with the symbol db/id in the map >>> held by the var *data-readers* and passes to it the result of parsing >>> the rest of the literal (a vector holding the keyword :db.part/db in >>> this case). Importantly, this function is not pure and the integer it >>> uses will be different on each invocation. (Given this form of the >>> #db/id literal; you can also specify a particular number yourself -- >>> #db/id [:db.part/db some-number-here].) >>> >>> In any case, once the reader reads in your code including some >>> particular id, the compiler will compile the result preserving the >>> particular values it sees, so it will embed code to construct *exactly >>> this* id in the compiled output. Thus you end up with a particular id >>> hardwired into the first version of your function. >>> >>> With the second version, if you invoke it multiple times at the REPL, >>> you ask the reader for a new id at each invocation, so it works as you >>> expect. If instead you were to use it inside a function like so: >>> >>> (defn foo [] >>> (make-column-schema #db/id [:db.part/db] :results/subject >>> :db.type/string)), >>> >>> then again the same id would be used for every (foo) call. >>> >>> Cheers, >>> Michał >>> >>> >>> On 3 March 2013 21:58, <edw...@kenworthy.info> wrote: >>> > So, I am studying a piece of code from the web. I've dissected most of >>> it >>> > and am in the process of re-factoring it. >>> > >>> > What I don't understand is why one version works and the other >>> doesn't. >>> > >>> > So for both: >>> > >>> > (ns gcse-results.core (:use [datomic.api :only [q db] :as d]) (:use >>> > quil.core)) >>> > >>> > This doesn't work: >>> > >>> > (defn make-column-schema [db-ident db-type] >>> > {:db/id #db/id[:db.part/db] >>> > :db/ident db-ident >>> > :db/valueType db-type >>> > :db/cardinality :db.cardinality/one >>> > :db.install/_attribute :db.part/db}) >>> > >>> > Each call to: >>> > >>> > (make-column-schema :results/subject :db.type/string) >>> > >>> > The value of #db/id[:db.part/db] is the same. >>> > >>> > And this works: >>> > >>> > (defn make-column-schema [db-id db-ident db-type] >>> > {:db/id db-id >>> > :db/ident db-ident >>> > :db/valueType db-type >>> > :db/cardinality :db.cardinality/one >>> > :db.install/_attribute :db.part/db}) >>> > >>> > Each call to: (make-column-schema #db/id[:db.part/db] :results/subject >>> > :db.type/string) >>> > >>> > The value of #db/id[:db.part/db] is the different, as expected. >>> > >>> > Now I thought that I understood #db/id[:db.part/db] (call to a Java >>> > constructor) but obviously my understanding is flawed as I would >>> expect both >>> > of these functions to produce the same thing, but they don't so >>> there's >>> > obviously some gap in my understanding. >>> > >>> > Help? >>> > >>> > -- >>> > -- >>> > You received this message because you are subscribed to the Google >>> > Groups "Clojure" group. >>> > To post to this group, send email to clo...@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+u...@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 unsubscribe from this group and stop receiving emails from it, send >>> an >>> > email to clojure+u...@googlegroups.com. >>> > For more options, visit https://groups.google.com/groups/opt_out. >>> > >>> > >>> >>
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