# Phooey

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== Abstract == | == Abstract == | ||

− | '''Phooey''' is a functional UI library for [[Haskell]]. | + | '''Phooey''' is a functional UI library for [[Haskell]]. Or it's two of them, as it provides a <hask>Monad</hask> interface ''and'' an <hask>Applicative</hask> interface. The simplicity of Phooey's implementation is due to its use of [[Reactive]] for applicative, data-driven computation. (Before version 2.0, Phooey used the [[DataDriven]] library.) |

− | * Read [http:// | + | Besides this wiki page, here are more ways to find out about Phooey: |

− | * Get the code repository: '''<tt>darcs get http:// | + | * Read [http://hackage.haskell.org/package/phooey-2.0 the Haddock docs] (with source code, additional examples, and Comment/Talk links). |

− | + | * Get the code repository: '''<tt>darcs get http://conal.net/repos/phooey</tt>'''. | |

− | + | ||

+ | The package can be installed from [[Hackage]], using [[cabal-install]]: | ||

+ | cabal install phooey | ||

Phooey is also used in [[GuiTV]], a library for composable interfaces and "tangible values". | Phooey is also used in [[GuiTV]], a library for composable interfaces and "tangible values". | ||

+ | |||

+ | Since Reactive is currently broken (as of February 2010), Phooey is also broken. | ||

== Introduction == | == Introduction == | ||

Line 14: | Line 18: | ||

GUIs are usually programmed in an unnatural style, in that implementation dependencies are inverted, relative to logical dependencies. This reversal results directly from the ''push'' (data-driven) orientation of most GUI libraries. While outputs depend on inputs from a user and semantic point of view, the ''push'' style imposes an implementation dependence of inputs on outputs. | GUIs are usually programmed in an unnatural style, in that implementation dependencies are inverted, relative to logical dependencies. This reversal results directly from the ''push'' (data-driven) orientation of most GUI libraries. While outputs depend on inputs from a user and semantic point of view, the ''push'' style imposes an implementation dependence of inputs on outputs. | ||

− | A second drawback of the push style is that it is ''imperative'' rather than declarative. A GUI program describes actions to update a model | + | A second drawback of the push style is that it is ''imperative'' rather than declarative. A GUI program describes actions to update a model and view in reaction to user input. In contrast to the ''how-to-update'' style of an imperative program, a functional GUI program would express ''what-it-is'' of a model in terms of the inputs and of the view in terms of the model. |

The questions of push-vs-pull and imperative-vs-declarative are related. While an imperative GUI program could certainly be written to pull (poll) values from input to model and model to view, thus eliminating the dependency inversion, I don't know how a declarative program could be written in the inverted-dependency style. ([[Talk:Phooey|Do you?]]). | The questions of push-vs-pull and imperative-vs-declarative are related. While an imperative GUI program could certainly be written to pull (poll) values from input to model and model to view, thus eliminating the dependency inversion, I don't know how a declarative program could be written in the inverted-dependency style. ([[Talk:Phooey|Do you?]]). | ||

− | A important reason for using push rather than pull in a GUI implementation is that push is typically much more efficient. A simple pull implementation would either waste time recomputing an unchanging model and view (pegging your CPU for no benefit), or deal with the complexity of avoiding that recomputation. The push style computes only when inputs change. ( | + | A important reason for using push rather than pull in a GUI implementation is that push is typically much more efficient. A simple pull implementation would either waste time recomputing an unchanging model and view (pegging your CPU for no benefit), or deal with the complexity of avoiding that recomputation. The push style computes only when inputs change. (Continuous change, i.e. animation, negates this advantage of push.) |

− | Phooey ("'''Ph'''unctional '''oo'''s'''e'''r '''y'''nterfaces") adopts the declarative style, in which outputs are expressed in terms of inputs. Under the hood, however, the implementation is push-based (data-driven). Phooey | + | Phooey ("'''Ph'''unctional '''oo'''s'''e'''r '''y'''nterfaces") adopts the declarative style, in which outputs are expressed in terms of inputs. Under the hood, however, the implementation is push-based (data-driven). Phooey uses the [[Reactive]] library to perform the dependency inversion invisibly, so that programmers may express GUIs simply and declaratively while still getting an efficient implementation. |

− | Phooey came out of [http://conal.net/Pajama Pajama] and [http://conal.net/papers/Eros Eros]. | + | Phooey came out of [http://conal.net/Pajama Pajama] and [http://conal.net/papers/Eros Eros]. Pajama is a re-implementation of the [http://conal.net/Pan Pan] language and compiler for function synthesis of interactive, continuous, infinite images. Pan and Pajama use a monadic style for specifying GUIs and are able to do so because they use the implementation trick of [http://conal.net/papers/jfp-saig Compiling Embedded Languages], in which one manipulates expressions rather than values. (This trick is mostly transparent, but the illusion shows through in places.) |

− | == One example, | + | == One example, two interfaces == |

As an example, below is a simple shopping list GUI. The <hask>total</hask> displayed at the bottom of the window always shows the sum of the values of the <hask>apples</hask> and <hask>bananas</hask> input sliders. When a user changes the inputs, the output updates accordingly. | As an example, below is a simple shopping list GUI. The <hask>total</hask> displayed at the bottom of the window always shows the sum of the values of the <hask>apples</hask> and <hask>bananas</hask> input sliders. When a user changes the inputs, the output updates accordingly. | ||

: [[Image:ui1.png]] | : [[Image:ui1.png]] | ||

− | Phooey presents | + | Phooey presents two styles of functional GUI interfaces, structured as a [[monad]] and as an [[applicative functor]]. (I have removed the original [[arrow]] interface.) Below you can see the code for the shopping list example in each of these styles. |

− | The examples below are all found under [http://darcs.haskell.org/packages/phooey/src/Examples <code>src/Examples/</code>] in the phooey distribution, in the modules [http://darcs.haskell.org/packages/phooey/src/Examples/Monad.hs <code>Monad | + | The examples below are all found under [http://darcs.haskell.org/packages/phooey/src/Examples <code>src/Examples/</code>] in the phooey distribution, in the modules [http://darcs.haskell.org/packages/phooey/src/Examples/Monad.hs <code>Monad.hs</code>], and [http://darcs.haskell.org/packages/phooey/src/Examples/Applicative.hs <code>Applicative.hs</code>]. In each case, the example is run by loading the corresponding example module into ghci and typing <hask>runUI ui1</hask>. |

=== Monad === | === Monad === | ||

− | Here is a definition for the GUI shown above, formulated in terms of Phooey's [http://darcs.haskell.org/packages/phooey/doc/html/Graphics-UI-Phooey-Monad.html | + | Here is a definition for the GUI shown above, formulated in terms of Phooey's monadic interface. See the [http://darcs.haskell.org/packages/phooey/doc/html/Graphics-UI-Phooey-Monad.html monad interface] and its [http://darcs.haskell.org/packages/phooey/doc/html/src.Graphics.UI.Phooey.Monad.hs.html source code]. |

<haskell> | <haskell> | ||

− | ui1 :: UI | + | ui1 :: UI () |

ui1 = title "Shopping List" $ | ui1 = title "Shopping List" $ | ||

do a <- title "apples" $ islider (0,10) 3 | do a <- title "apples" $ islider (0,10) 3 | ||

Line 50: | Line 54: | ||

type IWidget a = a -> UI (Source a) | type IWidget a = a -> UI (Source a) | ||

-- Output widget type | -- Output widget type | ||

− | type OWidget a = Source a -> UI | + | type OWidget a = Source a -> UI () |

islider :: (Int,Int) -> IWidget Int | islider :: (Int,Int) -> IWidget Int | ||

Line 57: | Line 61: | ||

</haskell> | </haskell> | ||

− | The <hask>Source</hask> type is a [[ | + | The <hask>Source</hask> type is a (data-driven) source of [[Reactive|time-varying values]]. (<hask>Source</hask> is a synonym for <hask>Reactive</hask>.) By using <hask>Source Int</hask> instead of <hask>Int</hask> for the type of <hask>a</hask> and <hask>b</hask> above, we do not have to rebuild the GUI every time an input value changes. |

The down side of using source types is seen in the <hask>showDisplay</hask> line above, which requires lifting. We could partially hide the lifting behind overloadings of <hask>Num</hask> and other classes (as in [http://conal.net/Fran Fran], [http://conal.net/Pan Pan], and other systems). Some methods, however, do not not have sufficiently flexible types (e.g., <hask>(==)</hask>), and the illusion becomes awkward. The <hask>Arrow</hask> and <hask>Applicative</hask> interfaces hide the source types. | The down side of using source types is seen in the <hask>showDisplay</hask> line above, which requires lifting. We could partially hide the lifting behind overloadings of <hask>Num</hask> and other classes (as in [http://conal.net/Fran Fran], [http://conal.net/Pan Pan], and other systems). Some methods, however, do not not have sufficiently flexible types (e.g., <hask>(==)</hask>), and the illusion becomes awkward. The <hask>Arrow</hask> and <hask>Applicative</hask> interfaces hide the source types. | ||

Line 79: | Line 83: | ||

And use them: | And use them: | ||

<haskell> | <haskell> | ||

− | ui1x :: UI | + | ui1x :: UI () |

ui1x = title "Shopping List" $ | ui1x = title "Shopping List" $ | ||

do a <- apples | do a <- apples | ||

Line 88: | Line 92: | ||

We can go point-free by using <hask>liftM2</hask> and <hask>(>>=)</hask>: | We can go point-free by using <hask>liftM2</hask> and <hask>(>>=)</hask>: | ||

<haskell> | <haskell> | ||

+ | -- Sum UIs | ||

+ | infixl 6 .+. | ||

+ | |||

+ | (.+.) :: Num a => UIS a -> UIS a -> UIS a | ||

+ | (.+.) = liftA2 (liftA2 (+)) | ||

+ | |||

fruit :: UI (Source Int) | fruit :: UI (Source Int) | ||

− | fruit = | + | fruit = apples .+. bananas |

− | ui1y :: UI | + | ui1y :: UI () |

ui1y = title "Shopping List" $ fruit >>= total | ui1y = title "Shopping List" $ fruit >>= total | ||

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</haskell> | </haskell> | ||

=== Applicative Functor === | === Applicative Functor === | ||

− | [[Applicative functor]]s provide still another approach to separating static and dynamic information. Here is our example, showing just the changes relative to the [[#Monad|monadic]] version. (See the | + | [[Applicative functor]]s (AFs) provide still another approach to separating static and dynamic information. Here is our example, showing just the changes relative to the [[#Monad|monadic]] version. (See the |

− | [http://darcs.haskell.org/packages/phooey/doc/html/Graphics-UI-Phooey-Applicative.html Applicative interface doc] | + | [http://darcs.haskell.org/packages/phooey/doc/html/Graphics-UI-Phooey-Applicative.html Applicative interface doc] and its [http://darcs.haskell.org/packages/phooey/doc/html/src.Graphics.UI.Phooey.Applicative.hs.html source code].) |

− | and its [http://darcs.haskell.org/packages/phooey/doc/html/src | + | |

<haskell> | <haskell> | ||

ui1 :: UI (IO ()) | ui1 :: UI (IO ()) | ||

Line 133: | Line 119: | ||

total = title "total" showDisplay | total = title "total" showDisplay | ||

</haskell> | </haskell> | ||

+ | I chose reversed AF application <hask>(<**>)</hask> rather than <hask>(<*>)</hask> so the fruit (argument) would be displayed above the total (function). | ||

The UI-building functions again have the same types as before, relative to these new definitions: | The UI-building functions again have the same types as before, relative to these new definitions: | ||

Line 147: | Line 134: | ||

* <hask>ui1</hask> is an IO-valued UI. | * <hask>ui1</hask> is an IO-valued UI. | ||

− | = | + | The applicative UI interface (<hask>Graphics.UI.Phooey.Applicative</hask>) is implemented as a very simple layer on top of the monadic interface, using type composition (from [[TypeCompose]]): |

+ | <haskell> | ||

+ | type UI = M.UI :. Source | ||

+ | </haskell> | ||

+ | Thanks to properties of <hask>O</hask>, this definition suffices to make <hask>UI</hask> an AF. | ||

− | + | == Layout == | |

− | + | ||

− | + | ||

− | + | By default, UI layout follows the order of the specification, with earlier-specified components above later-specified ones. This layout may be overridden by explicit layout functions. For instance, the following definitions form variations of <hask>ui1</hask> laid out from bottom to top and from left to right. | |

− | + | GUIs & code: | |

− | + | ||

− | + | : [[Image:UiB1.png]] | |

− | + | : [[Image:UiL1.png]] | |

− | |||

<haskell> | <haskell> | ||

− | + | uiB1 = fromBottom ui1 | |

− | + | uiL1 = fromLeft ui1 | |

− | + | ||

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</haskell> | </haskell> | ||

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− | + | We can also lay out a sub-assembly, as in <hask>ui3</hask> below | |

− | + | ||

− | + | : [[Image:Ui3.png]] | |

− | + | ||

− | + | ||

− | + | <haskell> | |

− | + | ui3 = fromBottom $ | |

+ | title "Shopping List" $ | ||

+ | fromRight fruit >>= total | ||

</haskell> | </haskell> | ||

− | + | == Event Examples == | |

− | + | ||

− | The | + | The shopping examples above demonstrate the simple case of outputs (<hask>total</hask>) as functions of varying inputs (<hask>apples</hask> and <hask>bananas</hask>). Events were hidden inside the implementation of [[Reactive#Data.Reactive|reactive values]]. |

− | < | + | |

− | + | ||

− | + | ||

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− | </ | + | |

+ | This section shows two classic functional GUI examples involving a visible notion of [[Reactive#Data.Reactive|events]]. | ||

− | === | + | === Counter === |

− | + | Here is simple counter, which increments or decrements when the "up" or "down" button is pressed. The example is from "[http://www.citeulike.org/user/conal/article/1617415 Structuring Graphical Paradigms in TkGofer]" | |

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− | + | : [[Image:Phooey-UpDown.png]] | |

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− | + | The first piece in making this counter is a button, having a specified value and a label. The button GUI's value is an ''event'' rather than a source: | |

<haskell> | <haskell> | ||

− | + | smallButton :: a -> String -> UI (Event a) | |

− | + | ||

</haskell> | </haskell> | ||

+ | To make the up/down counter, we'll want two such buttons, labeled "up" and "down". But with what values? The buttons won't know what the counter value is, but they will know how to change the value, so the events will be function-valued. The two events resulting from the two buttons are then merged into a single function-valued event via <hask>mappend</hask>. (If you're curious about events at this point, take a detour and [[Reactive#Data.Reactive|read about them]].) | ||

− | + | The pair of buttons and combined event could be written as follows: | |

<haskell> | <haskell> | ||

− | + | upDown :: Num a => UIE (a -> a) | |

− | + | upDown = do up <- smallButton (+ 1) "up" | |

− | + | down <- smallButton (subtract 1) "down" | |

+ | return (up `mappend` down) | ||

</haskell> | </haskell> | ||

− | + | If you've been hanging around with monad hipsters, you'll know that we can write this definition more simply: | |

− | + | ||

<haskell> | <haskell> | ||

− | + | upDown = liftM2 mappend (smallButton (+ 1) "up") | |

+ | (smallButton (subtract 1) "down") | ||

</haskell> | </haskell> | ||

+ | Personally, I'm on an <hask>Applicative</hask> kick lately, so I prefer <hask>liftA2</hask> in place of <hask>liftM2</hask>. | ||

− | + | Still more sleekly, let's hide the <hask>liftM2</hask> (or <hask>liftA2</hask>) by using the <hask>Monoid (UI o) </hask> instance, which holds whenever <hask>Monoid o</hask>. | |

<haskell> | <haskell> | ||

− | + | upDown = smallButton (+ 1) "up" `mappend` | |

+ | smallButton (subtract 1) "down" | ||

</haskell> | </haskell> | ||

− | + | To finish the counter, use the <hask>accumR</hask> function, which makes a source from an initial value and an function-valued event. The source begins as the initial value and grows by applying the functions generated by the event. | |

− | + | ||

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− | The | + | |

<haskell> | <haskell> | ||

− | + | accumR :: a -> UI (Event (a -> a)) -> UI (Source a) | |

− | + | counter :: UI () | |

+ | counter = title "Counter" $ fromLeft $ | ||

+ | do e <- upDown | ||

+ | showDisplay (0 `accumR` e) | ||

</haskell> | </haskell> | ||

− | + | === Calculator === | |

− | + | The second event example is a calculator, as taken from "[http://citeseer.ist.psu.edu/vullinghs95lightweight.html Lightweight GUIs for Functional Programming]". | |

+ | : [[Image:Calc.png]] | ||

− | + | The basic structure of this example is just like the previous one. Each key has a function-valued event, and the keys are combined (visually and semantically) using <hask>mappend</hask>. | |

− | + | ||

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+ | First a single key. For variety, we'll postpone interpreting the key's event as a function. | ||

<haskell> | <haskell> | ||

− | + | key :: Char -> UIE Char | |

− | + | key c = button' c [c] | |

</haskell> | </haskell> | ||

− | + | We'll combine keys with the help of a friend of <hask>concatMap</hask>: | |

− | We | + | |

− | + | ||

− | : | + | |

− | + | ||

<haskell> | <haskell> | ||

− | + | mconcatMap :: Monoid b => (a -> b) -> [a] -> b | |

− | + | mconcatMap f = mconcat . map f | |

− | + | ||

</haskell> | </haskell> | ||

− | = | + | With this helper, it's especially easy to turn several keys into a row and several rows into a keyboard. |

+ | <haskell> | ||

+ | row :: [Char] -> UIE Char | ||

+ | row = fromLeft . mconcatMap key | ||

− | + | rows :: [[Char]] -> UIE Char | |

+ | rows = fromTop . mconcatMap row | ||

− | : [ | + | calcKeys :: UIE Char |

+ | calcKeys = rows [ "123+" | ||

+ | , "456-" | ||

+ | , "789*" | ||

+ | , "C0=/" ] | ||

+ | </haskell> | ||

− | + | Next, let's turn <hask>calcKeys</hask>'s character-valued event into a function-valued event. While the state of the [[Phooey#Counter|counter]] was a single number, the calculator state is a little more complicated. It consists of a number being formed and a continuation. | |

<haskell> | <haskell> | ||

− | + | type CState = (Int, Int -> Int) | |

− | + | ||

− | + | startCS :: CState | |

− | + | startCS = (0, id) | |

− | + | ||

</haskell> | </haskell> | ||

− | + | Keyboard characters have interpretations as state transitions. | |

<haskell> | <haskell> | ||

− | + | cmd :: Char -> CState -> CState | |

− | + | cmd 'C' _ = startCS | |

+ | cmd '=' (d,k) = (k d, const (k d)) | ||

+ | cmd c (d,k) | isDigit c = (10*d + ord c - ord '0', k) | ||

+ | | otherwise = (0, op c (k d)) | ||

+ | |||

+ | op :: Char -> Int -> Int -> Int | ||

+ | op c = fromJust (lookup c ops) | ||

where | where | ||

− | + | ops :: [(Char, Binop Int)] | |

− | + | ops = [('+',(+)), ('-',(-)), ('*',(*)), ('/',div)] | |

− | + | </haskell> | |

− | + | ||

− | + | ||

− | + | To compute the (reactive) value, from a key-generating event, accumulate transitions, starting with the initial state, and extract the value. | |

− | + | <haskell> | |

+ | compCalc :: Event Char -> Source Int | ||

+ | compCalc key = fmap fst (startCS `accumR` fmap cmd key) | ||

</haskell> | </haskell> | ||

− | + | Show the result: | |

<haskell> | <haskell> | ||

− | + | showCalc :: Event Char -> UI () | |

− | + | showCalc = title "result" . showDisplay . compCalc | |

− | + | ||

− | + | ||

− | + | ||

− | + | ||

</haskell> | </haskell> | ||

− | The | + | The whole calculator then snaps together: |

− | : | + | |

− | + | ||

<haskell> | <haskell> | ||

− | + | calc :: UI () | |

− | + | calc = title "Calculator" $ calcKeys >>= showCalc | |

− | + | ||

− | + | ||

− | + | ||

</haskell> | </haskell> | ||

− | |||

− | |||

== Portability == | == Portability == | ||

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wxHaskell is therefore built on top of [http://www.wxwidgets.org wxWidgets] -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. | wxHaskell is therefore built on top of [http://www.wxwidgets.org wxWidgets] -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X. | ||

</blockquote> | </blockquote> | ||

− | So I expect that Phooey runs on all of these platforms. That said, I have only tried Phooey on Windows. Please give it a try and leave a message on the Talk page | + | So I expect that Phooey runs on all of these platforms. That said, I have only tried Phooey on Windows. Please give it a try and leave a message on the [[Talk:Phooey|talk page]]. |

== Known problems == | == Known problems == | ||

Line 345: | Line 302: | ||

* Use Javascript and HTML in place wxHaskell, and hook it up with [[Yhc/Javascript]]. | * Use Javascript and HTML in place wxHaskell, and hook it up with [[Yhc/Javascript]]. | ||

− | [[Category:User | + | [[Category:User interfaces]] |

[[Category:Arrow]] | [[Category:Arrow]] | ||

[[Category:Monad]] | [[Category:Monad]] | ||

[[Category:Libraries]] | [[Category:Libraries]] | ||

[[Category:Packages]] | [[Category:Packages]] | ||

+ | [[Category:wxHaskell]] |

## Latest revision as of 14:34, 3 April 2012

## Contents |

## [edit] 1 Abstract

**Phooey**is a functional UI library for Haskell. Or it's two of them, as it provides a

*and*an

Besides this wiki page, here are more ways to find out about Phooey:

- Read the Haddock docs (with source code, additional examples, and Comment/Talk links).
- Get the code repository:
.`darcs get http://conal.net/repos/phooey`

The package can be installed from Hackage, using cabal-install:

cabal install phooey

Phooey is also used in GuiTV, a library for composable interfaces and "tangible values".

Since Reactive is currently broken (as of February 2010), Phooey is also broken.

## [edit] 2 Introduction

GUIs are usually programmed in an unnatural style, in that implementation dependencies are inverted, relative to logical dependencies. This reversal results directly from the *push* (data-driven) orientation of most GUI libraries. While outputs depend on inputs from a user and semantic point of view, the *push* style imposes an implementation dependence of inputs on outputs.

A second drawback of the push style is that it is *imperative* rather than declarative. A GUI program describes actions to update a model and view in reaction to user input. In contrast to the *how-to-update* style of an imperative program, a functional GUI program would express *what-it-is* of a model in terms of the inputs and of the view in terms of the model.

The questions of push-vs-pull and imperative-vs-declarative are related. While an imperative GUI program could certainly be written to pull (poll) values from input to model and model to view, thus eliminating the dependency inversion, I don't know how a declarative program could be written in the inverted-dependency style. (Do you?).

A important reason for using push rather than pull in a GUI implementation is that push is typically much more efficient. A simple pull implementation would either waste time recomputing an unchanging model and view (pegging your CPU for no benefit), or deal with the complexity of avoiding that recomputation. The push style computes only when inputs change. (Continuous change, i.e. animation, negates this advantage of push.)

Phooey ("**Ph**unctional **oo**s**e**r **y**nterfaces") adopts the declarative style, in which outputs are expressed in terms of inputs. Under the hood, however, the implementation is push-based (data-driven). Phooey uses the Reactive library to perform the dependency inversion invisibly, so that programmers may express GUIs simply and declaratively while still getting an efficient implementation.

Phooey came out of Pajama and Eros. Pajama is a re-implementation of the Pan language and compiler for function synthesis of interactive, continuous, infinite images. Pan and Pajama use a monadic style for specifying GUIs and are able to do so because they use the implementation trick of Compiling Embedded Languages, in which one manipulates expressions rather than values. (This trick is mostly transparent, but the illusion shows through in places.)

## [edit] 3 One example, two interfaces

As an example, below is a simple shopping list GUI. ThePhooey presents two styles of functional GUI interfaces, structured as a monad and as an applicative functor. (I have removed the original arrow interface.) Below you can see the code for the shopping list example in each of these styles.

The examples below are all found under`src/Examples/`

in the phooey distribution, in the modules `Monad.hs`

, and `Applicative.hs`

. In each case, the example is run by loading the corresponding example module into ghci and typing ### [edit] 3.1 Monad

Here is a definition for the GUI shown above, formulated in terms of Phooey's monadic interface. See the monad interface and its source code.

ui1 :: UI () ui1 = title "Shopping List" $ do a <- title "apples" $ islider (0,10) 3 b <- title "bananas" $ islider (0,10) 7 title "total" $ showDisplay (liftA2 (+) a b)

The relevant library declarations:

-- Input widget type (with initial value) type IWidget a = a -> UI (Source a) -- Output widget type type OWidget a = Source a -> UI () islider :: (Int,Int) -> IWidget Int showDisplay :: Show a => OWidget a title :: String -> UI a -> UI a

Before we move on to other interface styles, let's look at some refactorings. First pull out the slider minus initial value:

sl0 :: IWidget Int sl0 = islider (0,10)

Then the titled widgets:

apples, bananas :: UI (Source Int) apples = title "apples" $ sl0 3 bananas = title "bananas" $ sl0 7 total :: Num a => OWidget a total = title "total" . showDisplay

And use them:

ui1x :: UI () ui1x = title "Shopping List" $ do a <- apples b <- bananas total (liftA2 (+) a b)

-- Sum UIs infixl 6 .+. (.+.) :: Num a => UIS a -> UIS a -> UIS a (.+.) = liftA2 (liftA2 (+)) fruit :: UI (Source Int) fruit = apples .+. bananas ui1y :: UI () ui1y = title "Shopping List" $ fruit >>= total

### [edit] 3.2 Applicative Functor

Applicative functors (AFs) provide still another approach to separating static and dynamic information. Here is our example, showing just the changes relative to the monadic version. (See the Applicative interface doc and its source code.)

ui1 :: UI (IO ()) ui1 = title "Shopping List" $ fruit <**> total fruit :: UI Int fruit = liftA2 (+) apples bananas total :: Num a => OWidget a total = title "total" showDisplay

The UI-building functions again have the same types as before, relative to these new definitions:

type IWidget a = a -> UI a type OWidget a = UI (a -> IO ())

Notes:

- Output widgets are function-valued UI.
- has a simpler definition, requiring only one lifting instead of two.fruit
- is subtly different, because output widgets are nowtotal
*function-valued*. - uses the reverse application operatorui1. This reversal causes the function to appear after (below) the argument.(<**>)
- is an IO-valued UI.ui1

type UI = M.UI :. Source

## [edit] 4 Layout

By default, UI layout follows the order of the specification, with earlier-specified components above later-specified ones. This layout may be overridden by explicit layout functions. For instance, the following definitions form variations ofGUIs & code:

uiB1 = fromBottom ui1 uiL1 = fromLeft ui1

ui3 = fromBottom $ title "Shopping List" $ fromRight fruit >>= total

## [edit] 5 Event Examples

The shopping examples above demonstrate the simple case of outputs (This section shows two classic functional GUI examples involving a visible notion of events.

### [edit] 5.1 Counter

Here is simple counter, which increments or decrements when the "up" or "down" button is pressed. The example is from "Structuring Graphical Paradigms in TkGofer"

The first piece in making this counter is a button, having a specified value and a label. The button GUI's value is an *event* rather than a source:

smallButton :: a -> String -> UI (Event a)

The pair of buttons and combined event could be written as follows:

upDown :: Num a => UIE (a -> a) upDown = do up <- smallButton (+ 1) "up" down <- smallButton (subtract 1) "down" return (up `mappend` down)

If you've been hanging around with monad hipsters, you'll know that we can write this definition more simply:

upDown = liftM2 mappend (smallButton (+ 1) "up") (smallButton (subtract 1) "down")

upDown = smallButton (+ 1) "up" `mappend` smallButton (subtract 1) "down"

accumR :: a -> UI (Event (a -> a)) -> UI (Source a) counter :: UI () counter = title "Counter" $ fromLeft $ do e <- upDown showDisplay (0 `accumR` e)

### [edit] 5.2 Calculator

The second event example is a calculator, as taken from "Lightweight GUIs for Functional Programming".

The basic structure of this example is just like the previous one. Each key has a function-valued event, and the keys are combined (visually and semantically) usingFirst a single key. For variety, we'll postpone interpreting the key's event as a function.

key :: Char -> UIE Char key c = button' c [c]

mconcatMap :: Monoid b => (a -> b) -> [a] -> b mconcatMap f = mconcat . map f

With this helper, it's especially easy to turn several keys into a row and several rows into a keyboard.

row :: [Char] -> UIE Char row = fromLeft . mconcatMap key rows :: [[Char]] -> UIE Char rows = fromTop . mconcatMap row calcKeys :: UIE Char calcKeys = rows [ "123+" , "456-" , "789*" , "C0=/" ]

type CState = (Int, Int -> Int) startCS :: CState startCS = (0, id)

Keyboard characters have interpretations as state transitions.

cmd :: Char -> CState -> CState cmd 'C' _ = startCS cmd '=' (d,k) = (k d, const (k d)) cmd c (d,k) | isDigit c = (10*d + ord c - ord '0', k) | otherwise = (0, op c (k d)) op :: Char -> Int -> Int -> Int op c = fromJust (lookup c ops) where ops :: [(Char, Binop Int)] ops = [('+',(+)), ('-',(-)), ('*',(*)), ('/',div)]

To compute the (reactive) value, from a key-generating event, accumulate transitions, starting with the initial state, and extract the value.

compCalc :: Event Char -> Source Int compCalc key = fmap fst (startCS `accumR` fmap cmd key)

Show the result:

showCalc :: Event Char -> UI () showCalc = title "result" . showDisplay . compCalc

The whole calculator then snaps together:

calc :: UI () calc = title "Calculator" $ calcKeys >>= showCalc

## [edit] 6 Portability

Phooey is built on wxHaskell. Quoting from the wxHaskell home page,

wxHaskell is therefore built on top of wxWidgets -- a comprehensive C++ library that is portable across all major GUI platforms; including GTK, Windows, X11, and MacOS X.

So I expect that Phooey runs on all of these platforms. That said, I have only tried Phooey on Windows. Please give it a try and leave a message on the talk page.

## [edit] 7 Known problems

- Recursive examples don't work (consumes memory) in the Arrow or Applicative interface.

## [edit] 8 Plans

- Use Javascript and HTML in place wxHaskell, and hook it up with Yhc/Javascript.