What is FRP?

FRP is presented as a functional way to handle user input and GUI updates. Its core idea is that some values change over time, and these time-varying values are called signals. In Elm, signals update automatically and can be combined to build interactive behavior.

Reading notes

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• FRP is described as a functional setting for rich interaction, especially for handling user input and updating a GUI.
• The text says FRP makes it easier to create interactive GUIs and work with sequences of synchronous and asynchronous events.
• A signal is a value that changes over time, and FRP treats such values as updating automatically.
• Mouse.position is used as an example of a signal that changes when the mouse moves.
• Window.dimensions is another signal example that changes when the window is resized.
• count is shown counting how many times a signal updates, here used for mouse clicks.
• lift is used to apply a normal function to a signal so it runs automatically when the signal updates.
• The text says lifting a function that produces static graphics onto a signal produces animation.
• FRP becomes more powerful when paired with a graphics library, enabling interactive pages and purely functional games.
• FRP can combine multiple signals, such as using lift2 to relate mouse position to window width.
• sampleOn is described as sampling one signal whenever another signal updates.
• keepWhen keeps a signal’s value only when a boolean signal is true, and uses a default value so the result always has a value.
• The text describes FRP as declarative because it focuses on what is displayed rather than how the computer performs the updates.
• It contrasts FRP with traditional GUI frameworks that require event handlers, callbacks, and DOM manipulations.
• The page says FRP leaves many irrelevant details to the compiler, reducing the work needed for GUI programming.