Talk from JavaOne 2016. Screen capture available under https://youtu.be/CZr8RLJsZqc .

1. Adventures with Extreme Types in a Purely Functional Language
FregeFX:
Pure Functions and
Explicit Effects for JavaFX
JavaOne 2016

2. Dierk König
canoo
mittie

3. Frege is a Haskell for the JVM

4. Extreme Types
pure functions cannot produce an effect
but we have to!
-> produce actions that tell what to do
(like a recipe)
actions are of a special type, e.g.
IO actions or JFX actions

5. Extreme Types
make implicit constraints explicit
JavaFX:
only touch nodes inside UI thread
only do IO outside UI thread
Less tricky
errors

6. Developer
Discipline
Pure
Functional
Language

7. Constrained Context

8. Enforced by Compiler
Less tricky
errors

9. pure native encode java.net.URLEncoder.encode :: String -> String
encode “Dierk König“
native println System.out.println :: String -> IO ()
println “Dierk König“
native getText :: TextInputControl -> JFX String
text <- inputField.getText
println text - - does not compile!
inIO text println - - compiles!
Native Declarations

17. Entry Points I
The github project
https://github.com/Frege/FregeFX
The tutorial that uses FregeFX to build a
cover-flow gallery
https://github.com/Dierk/fregeTutorial
FregeChat, client written in FregeFX
https://github.com/Dierk/FregeChat

18. Entry Points II
Gui of the Frege REPL, written in FregeFX
https://github.com/Dierk/frepl-gui
some videos
- https://www.youtube.com/watch?v=pxKJ_KPLml
- https://www.youtube.com/watch?v=9V7w-RSC_1A

19. Unique in Frege
Global type inference (requires purity)
Purity by default
effects are explicit in the type system
Type-safe concurrency & parallelism
Laziness by default
Values are always immutable
Guarantees extend into Java calls

20. Why Frege
it is just a pleasure to work with

21. How?
http://www.frege-lang.org
@fregelang
stackoverflow „frege“ tag
edX FP101 MOOC

22. Dierk König
canoo
mittie
Please give feedback!