EFFECT — do something with side effects

01The shape

EFFECT is where the work happens. It runs a function with the current value as input, and the result becomes the new value. The journal records the input and the output.

02Try it

03The law: associativity

EFFECTs compose. Doing A then B is the same as doing B then A, as long as the composition is well-defined. This is the same associativity as function composition. It means you can rearrange your code without changing the outcome — the substrate handles the reordering safely.

04What you can build

A reducer. A transformation pipeline. A worker. Anything that does work. The substrate is reactive: when an EFFECT runs, the journal records the result, listeners fire, and any cell that depends on this one re-runs its own EFFECT.

05Next

EFFECTs change the world. VIEWs read it without changing anything. Lesson 4: VIEW →