🔀 Create a guide on using and creating side effects. (#93)

* :memo: Explain why managed effects are useful.

* :memo: Write a short explainer on pure functions.

* :memo: Finish side effects guide.

* :wrench: Add side effects guide to generated pages.

2 files changed, 16 insertions, 11 deletions

diff --git a/examples/05-http-requests/README.md b/examples/05-http-requests/README.md
index 4a118e4..c5fe073 100644
--- a/examples/05-http-requests/README.md
+++ b/examples/05-http-requests/README.md
@@ -51,8 +51,8 @@ want the Lustre runtime to execute before the next invocation of the `view`
 function.
 
 > **Note**: notice how the type of `view` remains the same. In Lustre, your `view`
-> is always a [_pure function_](https://en.wikipedia.org/wiki/Pure_function) that
-> takes a model and returns the UI to be rendered: we never perform side effects
+> is always a [_pure function_](https://github.com/lustre-labs/lustre/blob/main/pages/hints/pure-functions.md)
+> that takes a model and returns the UI to be rendered: we never perform side effects
 > in the `view` function itself.
 
 ## HTTP requests as side effects
diff --git a/examples/06-custom-effects/README.md b/examples/06-custom-effects/README.md
index 99b90c5..0af61bd 100644
--- a/examples/06-custom-effects/README.md
+++ b/examples/06-custom-effects/README.md
@@ -7,11 +7,10 @@ this example we'll see how to create effects of our own using Lustre's
 [`effect.from`](https://hexdocs.pm/lustre/lustre/effect.html#from)
 function.
 
-Since we use effects to communicate with _external_ systems (like the
-browser or the Erlang VM) you'll find creating custom effects usually involves
-Gleam's [external
-functions](https://tour.gleam.run/everything/#advanced-features-externals). So
-be sure to read up on that!
+Since we use effects to communicate with _external_ systems (like the browser or
+the Erlang VM) you'll find creating custom effects usually involves Gleam's
+[external functions](https://tour.gleam.run/everything/#advanced-features-externals).
+So be sure to read up on that!
 
 > Gleam externals are part of its "foreign function interface", which is why
 > you'll typically see files with `ffi` in the name - like
@@ -20,8 +19,9 @@ be sure to read up on that!
 ## Accessing Browser Storage
 
 In this example, the external system we want to interact with is the browser's
-[local storage](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage). This way, we can write a message into the text input and it will
-still be there when we refresh the page. Handy!
+[local storage](https://developer.mozilla.org/en-US/docs/Web/API/Window/localStorage).
+This way, we can write a message into the text input and it will still be there
+when we refresh the page. Handy!
 
 The `view`, `update` and `init` functions should look pretty familiar by now, so
 let's focus on the functions that generate our custom effects.
@@ -58,9 +58,14 @@ Here, our effect is simpler. We tell the gleam compiler we don't need to use the
 pattern](https://tour.gleam.run/everything/#basics-discard-patterns). Then we
 write to local storage, and no more work needs to be done.
 
-You may be wondering, why bother using an effect if we aren't also going to update our program with the result? Why not just fire off `do_write_localstorage` directly from the `update` function or a custom event handler?
+You may be wondering, why bother using an effect if we aren't also going to update
+our program with the result? Why not just fire off `do_write_localstorage` directly
+from the `update` function or a custom event handler?
 
-Using effects has many benefits! It lets us implement our `update` and `view` functions as [pure functions](https://en.wikipedia.org/wiki/Pure_function). This makes them easier to test, allows for time-travel debugging, and even opens the door to easily porting them to [server components](https://hexdocs.pm/lustre/lustre/server_component.html).
+Using effects has many benefits! It lets us implement our `update` and `view`
+functions as [pure functions](https://github.com/lustre-labs/lustre/blob/main/pages/hints/pure-functions.md).
+This makes them easier to test, allows for time-travel debugging, and even opens
+the door to easily porting them to [server components](https://hexdocs.pm/lustre/lustre/server_component.html).
 
 ## Another note on message naming