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PropLang

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[[Category:User interfaces]] [[Category:Proposals]] [[Category:Libraries]]
A design for a GUI library which is more like Haskell and less like C. To be written over Gtk2Hs.
A design for a GUI library which is more like Haskell and less like C. To be written over Gtk2Hs.
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== Thoughts by ==
== Thoughts by ==
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Neil Mitchell, Duncan Coutts
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Neil Mitchell, some patches from Joachim Breitner, discussions and help from Duncan Coutts
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== The Var concept ==
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For a darcs repo see: http://www.cs.york.ac.uk/fp/darcs/proplang/
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This is the low level stuff, on which the library will be built
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In particular check out Sample.hs, I am particularly proud of the word count:
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data Var a = ...
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sb!text =< with1 (txt!text) (\x ->
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data Notify = ...
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"Word count: " ++ show (length $ words x))
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get :: Var a -> IO a
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== Overview ==
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set :: Var a -> a -> IO ()
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addNotify :: Var a -> (a -> IO ()) -> IO Notify
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remNotify :: Notify -> IO ()
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newVar :: a -> IO (Var a)
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There are events, you can register to be notified when an event fires by doing
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== A concrete implementation of Var ==
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event += handler
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One thing to avoid, global state that needs a specific init function
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There are variables, which have events which fire, and a value which you can set and get.
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data Var a = Var {value :: IORef a,
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variable <- newVar "value"
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notifyId :: IORef Integer,
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variable += handler
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notifys :: IORef [(Integer, a -> IO ())],
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variable -< "value"
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source :: IORef (Maybe Notify)}
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x <- getVal variable
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data Notify = Notify {notifyId :: Integer, notifys :: IORef [(Integer, a -> IO ())]}
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There are objects, objects have properties. A property is just a variable.
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newVar :: a -> IO (Var a)
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window!text += handler
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newVar x = do v <- newIORef x
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window!text -< "Titlebar text"
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n <- newIORef []
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c <- newIORef 0
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a <- newIORef Nothing
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return $ Var v c n a
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get :: Var a -> IO a
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There are bindings which relate variables.
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get var = readIORef (value var)
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set :: Var a -> a -> IO ()
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-- the window text is the variable
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set var x = do n <- readIORef (notifys var)
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window!text =<= variable
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writeIORef (value var) x
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-- the window text is the variable, but upppercase
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mapM_ (\(a,b) -> b x) n
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window!text =< with1 variable (map toUpper)
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-- combine the two texts to create the window text
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window!text =< with2 variable1 variable2 (++)
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addNotify :: Var a -> (a -> IO ()) -> IO Notify
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If any of the values on the RHS of a binding change, then the LHS is updated.
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addNotify var f = do n <- readIORef (notifys var)
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c <- readIORef (notifyId var)
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writeIORef (notifyId var) (c+1)
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writeIORef (notifys var) ((c, f) : n)
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return $ Notify c (notifys var)
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-
 
+
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remNotify :: Notify -> IO ()
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remNotify notify = do n <- readIORef (notifys notify)
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writeIORef (notifys notify) (filter (\x -> fst x /= notifyId notify) n)
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-
 
+
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== Object layering ==
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-
 
+
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textBox~text -< "test"
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filename <- newVar Nothing
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addNotify filename hatCover
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lbl~text =< with filename $ \x ->
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case x of
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Nothing -> "Select a file"
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Just x -> "Loaded: " ++ x
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-
 
+
-
 
+
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where
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-
 
+
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(~) :: GtkObject -> GtkProp -> Var a -- ignoring lots of details here
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(-<) :: Var a -> a -> IO ()
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(=<) :: Var a -> Action a b -> IO ()
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with :: Var a -> (a -> b) -> Action a b
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+
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== Implementation of Object Layering ==
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data Action a b = Action (Var a) (a -> b)
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with :: Var a -> (a -> b) -> Action a b
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with var f = Action var f
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+
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(-<) :: Var a -> a -> IO ()
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(-<) var val = set var val
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-
 
+
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(=<) :: Var a -> Action a -> IO ()
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(=<) dest (Act src f) = do srcOld <- readIORef (source dest)
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when (isJust srcOld) $ remNotify (fromJust srcOld)
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note <- addNotify src (\x -> set dest (f x))
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writeIORef (source dest) (Just note)
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-
 
+
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== Implementation of Gtk Layering ==
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-
 
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class TextProvider a where
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text :: a -> Var String
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instance TextProvider TextView where
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text x = ...
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txt :: TextView
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(!) :: a -> (a -> b) -> b
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object ! prop = prop object
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-
 
+
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txt!text :: Var String
+

Current revision

A design for a GUI library which is more like Haskell and less like C. To be written over Gtk2Hs.

Link: http://www.cse.unsw.edu.au/~chak/haskell/ports/

1 Thoughts by

Neil Mitchell, some patches from Joachim Breitner, discussions and help from Duncan Coutts

For a darcs repo see: http://www.cs.york.ac.uk/fp/darcs/proplang/

In particular check out Sample.hs, I am particularly proud of the word count: 

sb!text =< with1 (txt!text) (\x ->
    "Word count: " ++ show (length $ words x))

2 Overview

There are events, you can register to be notified when an event fires by doing 

event += handler

There are variables, which have events which fire, and a value which you can set and get. 

variable <- newVar "value"
variable += handler
variable -< "value"
x <- getVal variable

There are objects, objects have properties. A property is just a variable. 

window!text += handler
window!text -< "Titlebar text"

There are bindings which relate variables. 

-- the window text is the variable
window!text =<= variable
-- the window text is the variable, but upppercase
window!text =< with1 variable (map toUpper)
-- combine the two texts to create the window text
window!text =< with2 variable1 variable2 (++)

If any of the values on the RHS of a binding change, then the LHS is updated.

Retrieved from "http://www.haskell.org/haskellwiki/PropLang"

Categories: User interfaces | Proposals | Libraries