Frege is an open source programming language created in 2011.
#207on PLDB | 13Years Old | 223Repos |
git clone https://github.com/frege/frege
Frege is a non-strict, purely functional programming language for the Java virtual machine in the spirit of Haskell. It is considered a Haskell dialect or simply "a" Haskell for the Java virtual machine. Frege has a strong static type system with type inference. Read more on Wikipedia...
{--
This program displays the
current time on stdandard output
every other second.
-}
module examples.CommandLineClock where
data Date = native java.util.Date where
native new :: () -> IO (MutableIO Date) -- new Date()
native toString :: Mutable s Date -> ST s String -- d.toString()
--- 'IO' action to give us the current time as 'String'
current :: IO String
current = do
d <- Date.new ()
d.toString
{-
"java.lang.Thread.sleep" takes a "long" and
returns nothing, but may throw an InterruptedException.
This is without doubt an IO action.
public static void sleep(long millis)
throws InterruptedException
Encoded in Frege:
- argument type long Long
- result void ()
- does IO IO ()
- throws ... throws ....
-}
-- .... defined in frege.java.Lang
-- native sleep java.lang.Thread.sleep :: Long -> IO () throws InterruptedException
main args =
forever do
current >>= print
print "\r"
stdout.flush
Thread.sleep 999
{--
This program displays the
current time on standard output
every other second.
-}
module examples.CommandLineClock where
data Date = native java.util.Date where
native new :: () -> IO (MutableIO Date) -- new Date()
native toString :: Mutable s Date -> ST s String -- d.toString()
--- 'IO' action to give us the current time as 'String'
current :: IO String
current = do
d <- Date.new () -- reads system timer, hence IO
d.toString
main args =
forever do
current >>= print -- print formatted date
print "\r" -- followed by carriage return
stdout.flush -- make sure it's shown
Thread.sleep 999L -- wait 0.999 seconds
Feature | Supported | Example | Token |
---|---|---|---|
MultiLine Comments | ✓ | {- A comment -} | {- -} |
Comments | ✓ | -- A comment | |
Line Comments | ✓ | -- A comment | -- |
Type Inference | ✓ | ||
Semantic Indentation | X |