Frege is a Haskell for the JVM. The slides starts from the perspective of a java programmer.

1. Frege
https://github.com/Frege/frege
Frege is a Haskell for the JVM

2. FizzBuzz sample
public class FizzBuzz { // IMPERATIVE
public static void main(String[] args) {
for (int i = 1; i <= 100; i++) {
if (i % 15 == 0) {
System.out.println("FizzBuzz");
} else if (i % 3 == 0) {
System.out.println("Fizz");
} else if (i % 5 == 0) {
System.out.println("Buzz");
} else {
System.out.println(i);
}
}}}
2
module FizzBuzz where // FUNCTIONAL
fizzes = cycle ["", "", "fizz"] -- cycle :: [a] -> [a]
buzzes = cycle ["", "", "", "", "buzz"]
pattern = zipWith (++) fizzes buzzes -- zipWith:: (a -> b -> c) -> [a] -> [b] -> [c]
numbers = map show [1..] -- map :: (a -> b) -> [a] -> [b]
fizzbuzz = zipWith max pattern numbers -- max :: Ord a => a -> a -> a
main _ = do -- main :: [String] -> IO
for (take 100 fizzbuzz) println -- take :: [Int] -> [a] -> [a]
http://c2.com/cgi/wiki?FizzBuzzTest

3. FizzBuzz complexity
3
Imperative Functional
Conditionals 4 0
Operators 4 1
Nesting Level (3 zur Info) 0
McCabe:M= 8 1
https://de.wikipedia.org/wiki/McCabe-Metrik

4. Frege Syntax (Function)
--‘=‘ is a mathematical operator ( NO ASSIGNMENT )
one = 1 -- ‘public static Integer one = 1;‘
two = 2 -- ‘public static Integer two = 2;‘
oneTwoTuple = (one, two) -- ‘()‘ tuple constructor
assertTuple = oneTwoTuple == (1,2) -- ‘True‘
oneTwoList = [one, two] -- ‘[]‘ list constructor
assertList = oneTwoList == [1,2] -- ‘True‘
-- aset is a unique list
aset list = unique list -- type: ‘aset:: (Eq a) => [a] -> [a]‘
-- amap is a list of (key,value) tuples
amap keys values = zip keys values -- type: ‘amap :: [a] -> [b] -> [(a,b)]‘
amap2 f values = zip (map f values) values -- type: ‘amap2:: (b -> a) -> [b] -> [(a,b)]‘
unique [] = [] -- type: ‘unique:: (Eq a) => [a] -> [a]‘
unique (x:xs)
| elem x xs = unique xs
| otherwise = x : unique xs
naturals = [1..] -- type: ‘naturals::[Int]‘=[1,2,..,Int.MAX]
evens = [ x | x <- [1..], even x] -- type: ‘evens ::[Int]‘=[1,3,..,Int.MAX-1]
4https://dierk.gitbooks.io/fregegoodness/

5. Frege Syntax (Types)
-- interface Interface<A> {...}
class Interface a where
methode :: a -> a -> Bool
-- interface DomainInterface {...}
data DomainInterface =
DomainIntImpl { int::Int } --class DomainIntImpl implements DomainInterface{ }
| DomainStringImpl{string::String}--class DomainStrImpl implements DomainInterface{ }
derive Show DomainInterface --class DomainIntImpl{ @Overwrite public String toString() }
--class DomainStringImpl{@Overwrite public String toString() }
instance Interface DomainInterface where
methode (DomainIntImpl {int=a}) (DomainIntImpl {int=b}) = a == b
methode (DomainStringImpl{string=a}) (DomainStringImpl {string=b}) = a == b
methode _ _ = False
-- class DomainIntImpl { @Overwrite public String methode(a,b)}
-- class DomainStringImpl { @Overwrite public String methode(a,b)}
ints = map DomainIntImpl [1..10] -- [ 1 , 2 ,.., 10 ]
strings = map DomainStringImpl $ map show [1..10] -- [“1“,“2“,..,“10“]
find_1_Int = head $ map (DomainIntImpl 1).methode ints -- True
find_1_String = head $ map (DomainStringImpl "1").methode strings -- True
5https://en.wikibooks.org/wiki/Haskell/Classes_and_types

6. Frege Syntax (Monad)
main _ = do // FUNCTIONAL
url <- URL.new "http://www.google.com" >>= either throw return
ios <- url.openStream >>= either throw return
rdr <- InputStreamReader.new ios "UTF-8" >>= either throw return
bfr <- BufferedReader.new rdr >>= either throw return
maybe <- bfr.readLine >>= println
ios.close
return()
6
public static void main(String[] args) { // IMPERATIVE
final URL url;
try { url = new URL("http://www.google.com");
} catch (MalformedURLException e) { throw new RuntimeException(e);}
final InputStream ios;
try { ios = url.openStream();
} catch (IOException e) {throw new RuntimeException(e);}
InputStreamReader rdr = new InputStreamReader(ios);
BufferedReader bfr = new BufferedReader(rdr);
String next = null;
try {
while((next = bfr.readLine()) != null){ System.out.println(next); }
} catch (IOException e) {throw new RuntimeException(e);}
try { ios.close();
} catch (IOException e) {throw new RuntimeException(e);}
}
http://www.learnyouahaskell.com/a-fistful-of-monads

7. Frege PROs
7
• Eleganz
• Pure Functional
• Thread Safe by Design
• Global Type inference
• Mvn, Gradle tooling exist
• Hoogle
http://de.slideshare.net/Mittie/frege-tutorial-at-javaone-2015

8. Frege CONs
8
• IDE (only eclipse :( )
• Compiler errors messages
• Debugging
• Laziness vs Performance
• Missing libraries

9. Blue or red pill?
9

10. Links
• GitHub: https://github.com/Frege
• Language: http://www.frege-lang.org/doc/Language.pdf
• Types: https://en.wikibooks.org/wiki/Haskell/Classes_and_types
• Monad: http://www.learnyouahaskell.com/a-fistful-of-monads
• EBook: https://dierk.gitbooks.io/fregegoodness/
• Video: http://www.yt.fully.pk/watch/1P1-HXNfFPc#
10