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.cursor/rules/vide/tut/crash-course/5-effect.md

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+# Effects
+
+Effects are functions that are ran in response to source updates.
+A source and effect is analogous to a signal and connection.
+
+Effects are created using `effect()`.
+
+```luau
+local source = vide.source
+local effect = vide.effect
+
+local count = source(0)
+
+effect(function()
+    print("count: " .. count())
+end)
+
+-- "count: 0" printed
+count(1)
+-- "count: 1" printed
+```
+
+Any source read inside an effect is tracked and will rerun the effect when
+that source is updated.
+
+The effect runs its callback once immediately to initially figure out what
+sources are being read.
+
+Derived sources are also tracked, it does not matter how deeply nested
+inside a function a source is.
+
+```luau
+local source = vide.source
+local effect = vide.effect
+
+local count = source(1)
+
+local doubled = function()
+    return count() * 2
+end
+
+effect(function()
+    print("doubled count: " .. doubled())
+end)
+
+-- "doubled count: 2" printed
+count(2)
+-- "doubled count: 4" printed
+```
+
+If a source is updated with the same value it already had, it will not rerun
+effects depending on it.
+
+You can also read from a source within an effect without the effect tracking it.
+
+```luau
+local source = vide.source
+local effect = vide.effect
+local untrack = vide.untrack
+
+local a = source(0)
+local b = source(0)
+
+effect(function()
+    print(`a: {a()} b: {untrack(b)}`)
+end)
+
+a(1) -- prints "a: 1 b: 0"
+b(1) -- prints nothing
+a(2) -- prints "a: 2 b: 1"
+```