frp.md

Overview

frp is used to:

• display things on screen
• react to input from keyboard and mouse
• prioritize which ui elements get inputs

frp works by going through a table of:

• "things that can happen", and
• "things that want to know what happened"

e.g.

@{mouse [flash-cursor-position]}

This means "whenever something mouse related happens, tell flash-cursor-position what happened".

In this context, mouse is an "emitter" as in "mouse emits things that happen".

flash-cursor-position is a "subscriber" as in "flash-cursor-position subscribes to things that happen".

Example usage

If freja is installed, the easiest way to figure out what "things that can happen" actually are, is to call:

(import freja/frp)

(frp/subscribe! frp/mouse pp)

If you are reading this in freja, you can put the cursor after each ) and hit Ctrl+Enter. Then try clicking somewhere and look in your terminal.

This means "the subscriber pp will be run whenever frp/mouse emits something".

In the above case, you would see these sorts of things in the terminal:

@[:press (234 472)]
@[:release (234 472)]

The above describes what the physical mouse did, like pressing a button, and at what pixel relative to the window the mouse did what it did. So @[:press (234 472)] means "the mouse button was pressed at x position 234 and y position 472". (0 0) would be the top left corner.

A "thing that can happen" is called an "event".

Available emitters

Freja's built-in emitters are listed below.

mouse

Emits events related to the physical mouse.

In the form of @[kind-of-event mouse-position] if not specified otherwise.

kind-of-event can be one of the following:

• :press
• :release
• :drag
• :double-click
• :triple-click
• :scroll - in the form of @[:scroll scroll-amount mouse-position], where scroll amount is how many pixels of scrolling occured and mouse-position is a tuple of the x/y coordinates relative to the window's top left corner.

Example

(import freja/frp)

(frp/subscribe! frp/mouse pp)

keyboard

Emits events related to the physical keyboard.

Always in the form of @[kind-of-event key]

kind-of-event can be one of the following:

• :key-down - is emitted when a key is pressed, or repeatedly when held for a certain period of time

key is a keyword corresponding to the physical button. This will not account for locale, e.g. if using dvorak and hitting physical n, you will get :n, not :b. This is due to how Raylib works internally.

Example

(import freja/frp)

(frp/subscribe! frp/keyboard pp)

chars

Emits events related to physical keyboard presses, respecting the locale of the user.

Always in the form of @[:char char]

char is a number corresponding to an ascii character. E.g. typing a emits @[:char 97].

Example

(import freja/frp)

(frp/subscribe! frp/chars pp)

callbacks

A stack of key -> callbacks, which will always only call the last callback for each key.

frame-chan

Emits an event each new frame.

rerender

Emits events when rerendering is needed.