add bit about function application with $

basics/01-values-and-functions.md

@@ -15,6 +15,7 @@
     - [`case` expressions](#case-expressions)
     - [Exercises (Asking questions about values)](#exercises-asking-questions-about-values)
       - [Exercise notes (Asking questions about values)](#exercise-notes-asking-questions-about-values)
+  - [Interlude: Function application with `$`](#interlude-function-application-with-)
   - [Partial application](#partial-application)
     - [Exercises (Partial application)](#exercises-partial-application)
       - [Exercise notes (Partial application)](#exercise-notes-partial-application)
@@ -483,6 +484,35 @@ action of type `IO ()` in each branch when we executed `putStrLn ...`.
 
 0. You don't need `if` for this one.
 
+## Interlude: Function application with `$`
+
+Sometimes you'll want to apply a function and you'll need to parenthesize the expression in order
+to do it:
+
+```haskell
+safeDivide :: Int -> Int -> DivisionResult
+safeDivide _x 0 = DivisionByZero
+safeDivide x divisor =
+  let xAsFloat = fromIntegral x
+      divisorAsFloat = fromIntegral divisor
+   -- We want to apply the `DivideSuccess` constructor here to the result of the
+   -- division, not just `xAsFloat`, so we parenthesize the calculation.
+   in DivideSuccess (xAsFloat / divisorAsFloat)
+```
+
+The above can be written using the `$` operator, which applies the function on the left to the
+expression on the right:
+
+```haskell
+safeDivide :: Int -> Int -> DivisionResult
+safeDivide _x 0 = DivisionByZero
+safeDivide x divisor =
+  let xAsFloat = fromIntegral x
+      divisorAsFloat = fromIntegral divisor
+   -- With `$` we no longer need to parenthesize the expression.
+   in DivideSuccess $ xAsFloat / divisorAsFloat
+```
+
 ## Partial application
 
 When you apply a function, you can choose to **not** pass all the arguments it's expecting. This