Clojure is a Lisp dialect that runs on the Java Virtual Machine (JVM). It was created in 2007 and focuses on functional programming and immutability. Clojure uses persistent data structures, which provide fast access and iteration while allowing for immutable updates. It supports concurrency through software transactional memory (STM) without locks.
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Clojure - Dynamic LISP on the JVM
1. Clojure
● LISP on the JVM
● Dynamic
● Started in 2007 by Rich Hickey
● 3 years of planning
● Current version - 1.6.0
● Eclipse license
2. Defining Features
● LISP syntax but not Common LISP or Scheme
– Macros
● Immutability
● Functional
● JVM based
– Java interop
– Not OOP
● Supports Concurrency
3. Syntax
● Numbers: 1234, 1.234, 1.234M
● Ratios: 22/7
● Strings: “foo”, “bar”, Characters: a b c
● Symbols: foo, bar, Keywords: :foo, :bar
● Boolean: true, false, Null: nil
● Regex Patterns: #”a*b”
5. Syntax
● That's the entire syntax
● Data strcuture are the code (Homoiconicity)
● All data literals stand for themselves except:
– Lists (IFn invocation)
– Symbols (“pointers”)
7. Persistent Data Structures
● All Clojure data structures are persistent
● Collections maintain performance guarantees:
– New + Old version of collections are available after
change
– New versions are not full copies
– Thread safe, iteration safe
● Sequences replace traditional lists
– All Clojure and Java collections can be made into
seqs
14. Concurrency
● Clojure uses STM – no locks in the code
– Multiversion Concurrency Control (MVCC)
– Readers never impede writers and writers never impeded
readers
● 3 primitive containers to store mutable data – atom, ref,
agent
– Refs – coordinated-sync access to many identities
– Atoms – Uncoordinated-sync access to a single identity
– Agents – Uncoordinated-async access to a single identity
15. So Much More...
● Metadata
● Optimized tail recursion
● Destructuring binding in let/fn/loop
● List comprehensions
● Multimethods
● Parallel computations
● Macros