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Clojure 1.1 And Beyond
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Clojure 1.1 And Beyond


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A rundown of the new features for Clojure v1.1 and expected features for v1.2 and beyond.

A rundown of the new features for Clojure v1.1 and expected features for v1.2 and beyond.

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  • 1. Clojure 1.1 and Beyond
  • 2. Deprecations watchers add-classpath ^ clojure.parallel clojure.lang.Repl, clojure.lang.Script
  • 3. Watchers Functions add-watcher and remove-watcher are gone. Replaced by add-watch and remove-watch. (def x (ref 0)) (add-watch x :change (fn [key r old new] (println old " -> " new))) (dosync (alter x inc)) ; 0 -> 1 ;=> 1 (remove-watch x :change) (dosync (alter x inc)) ;=> 2 highlight: clojure
  • 4. add-classpath Used to be able to do insane things like: (add-classpath "") (require '[prolog :as pro]) (pro/fact painter reynolds joshua english) (pro/db-query 'painter) ;=> ((reynolds joshua english)) highlight: clojure You should feel unclean by this. ^ Deprecated, use meta instead: (def x (with-meta [1 2] {:in-love? true})) ^x ;=> {:in-love? true} (meta x) ;=> {:in-love? true} highlight: clojure This is so that ^ can eventually become the type hint reader macro.
  • 5. clojure.parallel clojure.parallelis being re-worked to use the Java 7 fork-join library. You can track progress or contribute on Clojure's par branch. REPL and Scripts clojure.lang.Repl and clojure.lang.Script have been replaced by clojure.main. java -cp clojure.jar clojure.main # REPL java -cp clojure.jar clojure.main -i script.clj -r # REPL, load script.clj on startup java -cp clojure.jar clojure.main script.clj # Run script java -cp clojure.jar clojure.main -e '(+ 1 41)' # Eval string java -cp clojure.jar clojure.main - # Run with stdin highlight: clojure
  • 6. Additions Primitive Array Generation and Casting Chunked Sequences Futures Promises Transients Function pre- and post- conditions User-controlled Thread Bindings (not discussed) Ref History (not discussed) New Namespaces Miscellaneous
  • 7. Primitive Array Generation boolean-array, byte-array, char-array, and short-array (def x (byte-array [(byte 0x71) (byte 0x75) (byte 0x78)])) (String. x) ;=> "qux" highlight: clojure Primitive Array Casting booleans, bytes, chars, shorts
  • 8. Chunked Sequences Making sequence operations more efficient since v1.1! What is the Granularity of Laziness and Sequential Processing? Prior to 1.1 the answer was 1 element at a time. For 1.1 and beyond the answer is 1 chunk at a time.
  • 9. A Chunk at a Time
  • 10. Advantages of Chunkiness Still works on the 1-at-a-time model Aligns with the underlying data structures Amortizes the overhead of sequential access Once every 32 times Still avoids full realization Disadvantage Eliminates full laziness Although an API for 1-at-a-time laziness is in the works More Information
  • 11. Futures Asynchronous computations occuring in other threads that will block if the expression has not finished. All subsequent dereferencing will return the calculated value. (let [x (future (do (Thread/sleep 5000) (+ 41 1)))] @x) ; ... 5 seconds later ;=> 42 highlight: clojure Also useful: future-call, future?, future-done?, future-cancel, future-cancelled?. Promise / Deliver A hand-off reference used to deliver a value from one thread to another. Any attempt to dereference will block until "delivery". (def x (promise)) (.start (Thread. #(do (Thread/sleep 5000) (deliver x "Dear John")))) @x ; ... 5 seconds later ;=> "Dear John" highlight: clojure
  • 12. Transients Provides a mutable subset of functions to use on transient versions of the standard collection types. Used on locals only and only on vectors, hash-maps, and hash-sets Support the read-only functions transient, persistent!, conj!, assoc!, dissoc!, pop!, disj! to mutate Thread-safe. Modification attempt in a different thread throws an execption Here is a transient version of concat: (defn zen-cat [x y] (loop [src y, ret (transient x)] (if src (recur (next src) (conj! ret (first src))) (persistent! ret)))) (zen-cat [1 2 3] [4 5 6]) ;=> [1 2 3 4 5 6] highlight: clojure Rememeber to call persistent! before returning your transient only if you intend to give out a mutable version: (persistent! (conj! (zen-cat [1 2 3] [4 5 6]) 7)) ;; assume just ret on return ;=> [1 2 3 4 5 6 7] highlight: clojure
  • 13. :pre and :post Sets constraints on the input and output of a function. (defn constrained-fn [f x] {:pre [(pos? x)] :post [(= % (* 2 x))]} (f x)) (constrained-fn #(* 2 %) 2) ;=> 4 (constrained-fn #(* 2 %) -2) ; java.lang.AssertionError: Assert failed: (pos? x) (constrained-fn #(* 3 %) 2) ; java.lang.AssertionError: Assert failed: (= % (* 2 x)) highlight: clojure
  • 14. New Namespaces clojure.test clojure.test.junit clojure.stacktrace clojure.walk clojure.template
  • 15. Misc. juxt ((juxt a b c) x) => [(a x) (b x) (c x)] ((juxt + *)) ;=> [0 1] ((juxt - /) 2) ;=> [-2 1/2] highlight: clojure
  • 16. Clojure 1.2 (probably) reify deftype defprotocol Fine-grained locals clearing Agent error handlers Clojure 1.? Clojure in Clojure IO streams (not discussed) Chunked sequence API (not discussed) Program verification via Datalog (not discussed) Finger trees (read The Joy of Clojure)
  • 17. Reify -- aka newnew Like proxy, except: Only protocols or interfaces Method bodies are true methods and not external functions No dynamic swapping of methods Must be AOT'd Deftype Dynamically generates bytecode for an anonymous class with some fields and a type slot Might also generate methods for protocols or interfaces Can be AOT'd for extra benefits Like defstruct, except: Generates a class with fields, no map lookups Faster field lookup Has a proper type slot Fields can be primitive and hinted Can implement any number of protocols or interfaces More Information
  • 18. Protocols The best of interfaces Signatures only Multiple implements Without the mold Which interfaces to implement are defined along with the type Avoids isa/instanceof and heirarchies And Even Better Allows independent extension Single dispatch on type More Information
  • 19. Fine-grained Locals Clearing (let [r (range 1e9)] [(first r) (last r)]) ; java.lang.OutOfMemoryError: Java heap space highlight: clojure No need for strict tail-position adherence! More Information
  • 20. Agent Error Queues Since agent actions are run in other thread(s), what happens if exceptions are thrown? Currently Exceptions are stored in the agent itself and accessed/cleared by agent- errors/ clear-agent-errors Future Callbacks provided a queue of errors and react based on :continue and :fail error modes More information
  • 21. Clojure in Clojure (cinc) Clojure is three parts: 1. The compiler -- JAVA 2. The data structures -- JAVA (mostly) 3. clojure.core+ -- CLOJURE Clojure in Clojure is the effort to replace the Java bits above with Clojure without losing the JVM.
  • 22. Toward Clojure in Clojure reify is of the utmost importance We could use proxy and gen-class but too slow The compiler and reader could be written in Clojure today But first types and protocols should be rolled out
  • 23. Why Clojure in Clojure? Porting No need to port the structures Only (relatively) tiny bits of the compiler Description of Clojure's special forms Using the JVM to bootstrap other platform targets But What is Clojure? Too philosophical for this talk. More Information
  • 24. Questions? Order today with code 'j1337' and get a whopping 37% off!