Add source to show() callback

src/show.luau

@@ -1,16 +1,28 @@
-local switch = require "./switch"
+local derive = require "./derive"
+local untrack = require "./untrack"
 
-local function show<T>(source: () -> any, component: () -> T, fallback: (() -> T)?): () -> T?
-    local function truthy()
+local function show<T, U>(source: () -> T?, component: (() -> T) -> U, fallback: (() -> U)?): () -> U?
+    local truthy = derive(function()
         return not not source()
-    end
+    end)
 
-    return switch(truthy) {
-        [true] = component,
-        [false] = fallback,
-    }
+    -- seemingly redundant derivation to extend the reactive graph so that
+    -- the propogation of the source's update is delayed, giving time for
+    -- the show() scope to be destroyed before potential effects registered
+    -- by the component can run when they should not run
+    -- todo: are there cases this method does not cover?
+    local derived = derive(function()
+        return source()
+    end)
+
+    return derive(function()
+        return
+            if truthy() then untrack(function() return component(derived :: () -> T) end)
+            elseif fallback then untrack(fallback)
+            else nil
+    end)
 end
 
-return show ::
-    (<T>(source: () -> any, component: () -> T) -> () -> T?) &
-    (<T, U>(source: () -> any, component: () -> T, fallback: () -> U) -> () -> (T | U)?)
+return show :: (
+    ( <T, U>(source: () -> T?, component: (() -> T) -> U) -> () -> U? )
+)