Functional Eye for the Java Guy

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Functional Eye for the Java Guy
Convenor: Ben, Michael

Mike, Dimitry, Alexandro, giannis, Alexander, Elisabeth, Sven, Stefan, Aarne, Kirk, Rickard, Tasos, Michaelis, Andreas, John, Heinz and more


show of hands 10 people know

ugly code example

  • for "functional java"
  • 4 levels of nested classes
  • unreadable

issues with java

  • no native function types
  • all based around classes , class is smallest unit
  • SAM - Single Abstract Method (interface) (no state, one method)
  • inner classes (Class$Inner), hold on to outer class references
  • closing about context, final outer variables

when do you use FP

  • list comprehensions
  • composable functions
  • reusable code

OO vs. FP

  • OO -> box with state which contains method that change that state all the time
  • FP -> functions are transformations, side-effect free
  • higher order functions

what is the difference to methods in a object that just use ? -> still access to mutable object state/context

some examples in clojure

  • schwarz function (a bit too complex)
  • sorts a list by a user defined function
  • introduced defn, map, sort-by, lambdas, list, let, nth
  • simplified (sort-by f x)

Rickard :

  • Specification -> composable predicates that return boolean values -> usable for filtering
  • filter, map -> function applications to sequences/lists

smalltalk example by Kirk

  • if, while statement implemented using language constructs (blocks)

Partial audio recording

Audio recording


(as above)