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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 ==
  
Neil Mitchell, Duncan Coutts
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Neil Mitchell, some patches from Joachim Breitner, discussions and help from Duncan Coutts
  
== The Var concept ==
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For a darcs repo see: http://www.cs.york.ac.uk/fp/darcs/proplang/
  
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:
  
  data Var a = ...
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  sb!text =< with1 (txt!text) (\x ->
data Notify = ...
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    "Word count: " ++ show (length $ words x))
  
get :: Var a -> IO a
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== Overview ==
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
  
== A concrete implementation of Var ==
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event += handler
  
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.
  
  data Var a = Var {value :: IORef a,
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  variable <- newVar "value"
                  notifyId :: IORef Integer,
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variable += handler
                  notifys :: IORef [(Integer, a -> IO ())],
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variable -< "value"
                  source :: IORef (Maybe Notify)}
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x <- getVal variable
  
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.
  
  newVar :: a -> IO (Var a)
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  window!text += handler
  newVar x = do v <- newIORef x
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  window!text -< "Titlebar text"
              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.
get var = readIORef (value var)
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  set :: Var a -> a -> IO ()
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  -- the window text is the variable
  set var x = do n <- readIORef (notifys var)
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  window!text =<= variable
                writeIORef (value var) x
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-- the window text is the variable, but upppercase
                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
 +
window!text =< with2 variable1 variable2 (++)
  
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.
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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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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+
== Object layering ==
+
 
+
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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+
 
+
where
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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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+
 
+
== 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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+
(-<) :: Var a -> a -> IO ()
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(-<) var val = set var val
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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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Latest revision as of 21:21, 23 June 2007

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/

[edit] 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))

[edit] 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.