Effects and Coeffects

Effects.

They describe your program’s side-effects, (what your program does to the world).

Coeffects.

They track your program’s side-causes, (what your program requires from the world).

Declarative Effects pattern

• Event handlers are pure functions.
• They receive coeffects and return effects.
• Something else (a language run-time, a framework, etc.) is in charge of injecting the values that the coeffects track and interpreting the effects data to actually perform the side-effects they describe.
• That something else would be re-om in our case.

Related documents

• Built-in Coeffects in re-om
• Built-in Effects in re-om
• Registering custom effect handlers
• Registering custom coeffect handlers