Difference between revisions of "Grapefruit"

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[[Category:Libraries]]
 
[[Category:Libraries]]
 
[[Category:Arrow]]
 
[[Category:Arrow]]
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[[Category:Graphics]]
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[[Category:FRP]]
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[[Category:Packages]]
   
 
== About ==
 
== About ==
   
Grapefruit is a library for creating graphical user interfaces in a declarative way. It is currently based on [[Gtk2Hs]] but implementations on top of other GUI libraries are planned for the future.
 
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Grapefruit is a library for [[Functional Reactive Programming]] (FRP) with a focus on user interfaces. FRP makes it possible to implement reactive and interactive systems in a declarative style. With Grapefruit, user interfaces are described as networks of communicating widgets and windows. Communication is done via different kinds of signals which describe temporal behavior.
   
Grapefruit makes it possible to implement graphical user interfaces by describing them as systems of interconnected components. Components can be visible components like widgets and windows but also invisible components which provide certain control functionality. Component systems can be built from components by using methods from the <hask>Arrow</hask> and <hask>ArrowLoop</hask> classes.
 
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== Features ==
   
Components communicate via signals and event streams. A signal denotes a time-varying value, and an event stream denotes a sequence of events occuring at discrete points in time. Several functions allow the construction of signals and event streams in a purely functional manner.
 
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Grapefruit has the following important features:
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* a push-based FRP implementation where signals
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** can be memoized using ordinary variable bindings
  +
** can be merged without doubling of simultaneous events
  +
** cannot behave differently by starting them at different times
  +
* a record system which makes it possible that
  +
** input signals can be left out to get default behavior
  +
** output signals can be left out to ignore uninteresting data
  +
** output signals can be chosen and fetched by pattern matching
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* an abstract UI implementation which can work with different backends which in turn use different toolkits to provide different look and feel with one and the same application code (At the moment, the only supported UI toolkit is GTK+ (via [[Gtk2Hs]]). We plan to support Qt in the future, making use of the [[HQK]] project’s output.)
   
Grapefruit has also support for list signals, special signals denoting time-varying lists where each element has a unique identity. An algebra for list signals provides operations like concatenation, filtering and sorting. The key point is that when the value of a list signal changes, the values of the dependent list signals do not have to be recalculated completely but can be just updated to reflect the change.
 
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You might be interested in a [[Grapefruit/Comparison to other FRP libraries|comparison of Grapefruit to other FRP libaries]]
   
User interfaces with a changing collection of widgets are also possible with Grapefruit. There is a special widget which takes a list signal of widgets as its input and always contains the elements of it as its child widgets.
 
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== Installation ==
   
With Grapefruit, user interface descriptions always cover the complete lifetime of the respective interface. No explicit event handler registrations and no explicit recalculations of values are necessary. This is in line with the declarative nature of Haskell because it stresses how the user interface operates instead of how this operation is achieved. Internally though, signals and event streams are implemented efficiently using the event dispatching and handling mechanism of the underlying GUI toolkit.
 
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=== Released versions ===
   
The roots of Grapefruit lie in systems like [[Applications_and_libraries/GUI_libraries#FranTk|FranTk]] and [[Applications_and_libraries/GUI_libraries#wxFruit|wxFruit]]. Grapefruit tries to combine concepts of these systems with new ideas to become a system which maintains a reasonable balance between ease of use and efficiency.
 
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Grapefruit is released on [[Hackage]]. If you do not have special requirements, you can install Grapefruit by saying <code>cabal install grapefruit-ui-gtk grapefruit-examples</code>.
   
== Status ==
 
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If you do not have installed the <code>gtk</code> package yet, this command will also try to install this package. However, this will fail unless <code>gtk2hs-buildtools</code> is already installed. See the [http://projects.haskell.org/gtk2hs/ Gtk2Hs website] for further information.
   
As of July&nbsp;2007, Grapefruit is in an early stage. The basic concepts are implemented but the implementation is still subject to notable change.
 
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=== Development versions ===
   
Things planned for the next months cover the introduction of the model-view principle into Grapefruit as well as the development of a framework for animations. Furthermore, work on formal specification and verification of GUI properties based on Grapefruit’s GUI programming interface is about to start. This will probably be done using [[Ivor]] but it is intended to (also) use [[Epigram]] for this in the future.
 
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The source code of Grapefruit is on darcs hub at http://hub.darcs.net/jeltsch/grapefruit.
   
== Source code ==
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== Running the examples ==
   
The source code of Grapefruit resides inside a [[Darcs|darcs]] repository under http://softbase.org/grapefruit/darcs/main/. To get a copy, you can use the command <code><nowiki>darcs get http://softbase.org/grapefruit/darcs/main</nowiki></code>.
 
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You can run the examples by typing the following lines into GHCi:
   
== Documentation ==
 
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<blockquote><p><code>import Graphics.UI.Grapefruit.Circuit</code><br /><code>import Graphics.UI.Grapefruit.'''''UIBackend'''''</code><br /><code>import Examples.Grapefruit.'''''Example'''''</code><br /><code>run '''''UIBackend''''' mainCircuit ()</code></p></blockquote>
   
There is also documentation generated by [[Haddock]]. This documentation comes in two flavors. The [http://softbase.org/grapefruit/doc/api/ API documentation] covers only the public interface while the [http://softbase.org/grapefruit/doc/cif/ complete documentation] covers also the internals. Note that the documentation might be a bit out of date since it is not automatically regenerated on every commit yet.
 
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Replace <code>'''''Example'''''</code> with the name of the example to run and <code>'''''UIBackend'''''</code> with the name of the UI backend you want to use. At the moment, the only meaningful replacement for <code>'''''UIBackend'''''</code> is <code>GTK</code>. Possible replacements for <code>'''''Example'''''</code> are <code>Converter</code>, <code>ListView</code>, <code>SetView</code>, <code>Simple</code>, and <code>Switching</code>.
   
== Grapefruit-related Talks ==
 
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We do not provide ready-to-use executables since it is possible (at least in theory) to run the examples with different UI backends and an executable would be fixed to a specific backend.
   
* Wolfgang Jeltsch: Funktionale GUI-Programmierung in Haskell mit Grapefruit. Haskell in Leipzig 2. July 10, 2007.
 
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== Publications and talks ==
** [[Media:Grapefruit_HaL_2_presentation.pdf|presentation]] (in German)
 
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See [https://grapefruit-project.org/publications-and-talks the respective list] on [https://grapefruit-project.org/ the new Grapefruit website].
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== Community ==
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Grapefruit has a [http://projects.haskell.org/cgi-bin/mailman/listinfo/grapefruit mailing list] and a [http://trac.haskell.org/grapefruit/ project management website] where you can [http://trac.haskell.org/grapefruit/newticket report bugs], for example.
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== Screenshots ==
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Below are some screenshots from the examples of an earlier Grapefruit version. The Simple example is also available in the current version, along with several other examples not mentioned here.
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;Simple
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:Clicking on the button adds a star to the caption of the button. This doesn’t look very meaningful. However, Simple is actually a very important example since it demonstrates that feedbacks work—the output of the button is transformed and then used as the button’s input.
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:[[Image:Grapefruit-screenshot-Simple.png]]
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;Codebreaker
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:This is a Mastermind™-like game. The Add button is enabled if and only if the input field contains a valid code and the display box is enabled if and only if the list of guesses does not contain the code chosen by the computer. These properties are described in a declarative way in the source code.
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:[[Image:Grapefruit-screenshot-Codebreaker.png]]
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;CircuitingObjects
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:This example demonstrates Grapefruit’s support for animations.
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:[[Image:Grapefruit-screenshot-CircuitingObjects.png]]

Latest revision as of 15:20, 16 February 2017


About

Grapefruit is a library for Functional Reactive Programming (FRP) with a focus on user interfaces. FRP makes it possible to implement reactive and interactive systems in a declarative style. With Grapefruit, user interfaces are described as networks of communicating widgets and windows. Communication is done via different kinds of signals which describe temporal behavior.

Features

Grapefruit has the following important features:

  • a push-based FRP implementation where signals
    • can be memoized using ordinary variable bindings
    • can be merged without doubling of simultaneous events
    • cannot behave differently by starting them at different times
  • a record system which makes it possible that
    • input signals can be left out to get default behavior
    • output signals can be left out to ignore uninteresting data
    • output signals can be chosen and fetched by pattern matching
  • an abstract UI implementation which can work with different backends which in turn use different toolkits to provide different look and feel with one and the same application code (At the moment, the only supported UI toolkit is GTK+ (via Gtk2Hs). We plan to support Qt in the future, making use of the HQK project’s output.)

You might be interested in a comparison of Grapefruit to other FRP libaries

Installation

Released versions

Grapefruit is released on Hackage. If you do not have special requirements, you can install Grapefruit by saying cabal install grapefruit-ui-gtk grapefruit-examples.

If you do not have installed the gtk package yet, this command will also try to install this package. However, this will fail unless gtk2hs-buildtools is already installed. See the Gtk2Hs website for further information.

Development versions

The source code of Grapefruit is on darcs hub at http://hub.darcs.net/jeltsch/grapefruit.

Running the examples

You can run the examples by typing the following lines into GHCi:

import Graphics.UI.Grapefruit.Circuit
import Graphics.UI.Grapefruit.UIBackend
import Examples.Grapefruit.Example
run UIBackend mainCircuit ()

Replace Example with the name of the example to run and UIBackend with the name of the UI backend you want to use. At the moment, the only meaningful replacement for UIBackend is GTK. Possible replacements for Example are Converter, ListView, SetView, Simple, and Switching.

We do not provide ready-to-use executables since it is possible (at least in theory) to run the examples with different UI backends and an executable would be fixed to a specific backend.

Publications and talks

See the respective list on the new Grapefruit website.

Community

Grapefruit has a mailing list and a project management website where you can report bugs, for example.

Screenshots

Below are some screenshots from the examples of an earlier Grapefruit version. The Simple example is also available in the current version, along with several other examples not mentioned here.

Simple
Clicking on the button adds a star to the caption of the button. This doesn’t look very meaningful. However, Simple is actually a very important example since it demonstrates that feedbacks work—the output of the button is transformed and then used as the button’s input.
Grapefruit-screenshot-Simple.png
Codebreaker
This is a Mastermind™-like game. The Add button is enabled if and only if the input field contains a valid code and the display box is enabled if and only if the list of guesses does not contain the code chosen by the computer. These properties are described in a declarative way in the source code.
Grapefruit-screenshot-Codebreaker.png
CircuitingObjects
This example demonstrates Grapefruit’s support for animations.
Grapefruit-screenshot-CircuitingObjects.png