Hi Bill, Are your looking for something as simple as this:
(defrecord Foo [x]) (defn load-a-record-at-runtime "Loads a record value from a file" [f] (Foo. (slurp f))) Or is there some subtlety here? Stu > The confusion over type and instance was a sloppy example. Sorry. > > But in your solution I'm confused by one thing. You create and > instance of Foo in the let and then assoc the new value of List1 to > it. > This has two problems. One is that the loaded data is not > permanent. The other is that there is no way to add List2 to the > MyFoo record. > > (I've decided to not use MyFoo at all. Instead I have a (def List1 > (ref nil)) defined and then do a ref-set to it when the data is > loaded. This seems > much simpler and works. I then can do a def for List2, List3, etc.) > > It seem to me there should be some way to load a record at run time > without breaking the immutability laws. Once the dynamic data is > loaded, the record becomes immutable and will never be changed > again. It's unrealistic to imagine that we always know at compile > time what the values of a record will be. > I'm not a compiler person so I have no idea how to do such a thing and > no idea if it is possible. > > On Jul 27, 5:23 pm, Stuart Halloway <stuart.hallo...@gmail.com> wrote: >> Hi Bill, >> >> There are several issues here: >> >> (1) A confusion of record and instance. You are asking for the :list1 field >> from foo, the record type, not from an instance of the type. >> >> (:list1 foo) s/b (:list1 MyFoo) >> >> (2) You are ignoring the return value of assoc. Remember, Clojure data >> structures are immutable. To actually assign something you need to hold on >> to the return value of the expression (or use a reference type if you really >> want an identity). >> >> (3) The capitalization choices facilitate confusion. You are using "foo" for >> a record/class name, where both Java and Clojure style would dictate "Foo". >> Then you use "MyFoo" for a top-level def, where Clojure style would >> encourage "my-foo". >> >> The following code demonstrates these ideas. >> >> ;; stubbed so example can be run >> (defn load-data-from-file >> [x] :stub) >> >> (defrecord Foo [list1 list2]) >> >> (defn get-data [path] >> (let [list1Data (load-data-from-file path) >> f (Foo. nil nil) >> f (assoc f :list1 list1Data)] >> (:list1 f))) >> >> (get-data "fakepath") >> >> Regards, >> Stu >> >> Stuart Halloway >> Clojure/corehttp://clojure.com> All the examples of defrecord I see seem >> simple enough and when I >>> experiment in the REPL I get things to work as they should. However, >>> when I move to 'real' code I can't get it to work at all. >> >>> The problem at hand is simple enough - I want to create a record that >>> hold records. For example I have (defrecord foo [list1, list2]) >>> where list1 and list2 are defined records themselves. The issue is >>> that the data in list1 and list2 is dynamic - it is loaded from a file >>> at run time. So I do the following: >> >>> (def MyFoo (foo. nil nil)) >> >>> (defn get-data [path] >>> (let [list1Data (load-data-from-file path)] ; fill in the record >>> for list 1 >>> (assoc MyFoo :list1 list1Data) ; assign the data >>> record to the foo record >>> (:list1 foo) >>> )) >> >>> As I say, if I do this non-dynamically in the REPL I get the proper >>> result. >> >>> In my program (using let) (:list1 foo) always remains nil. What am >>> I doing wrong? And how can I get the fields of foo to take on the >>> dynamic data. >> >>> Bill >> >>> -- >>> 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 > > -- > 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 -- 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
