2.0: Pattern matching

Standard ML allow you to pattern match on values, providing case anaylsis. Using the list built into Standard ML, we could pattern match on its cases and apply a function to each value in the list.

• If the list is empty (case nil), there’s nothing to do: return the empty list.
• If the list has an item, x:
  • apply f to x
  • apply map f to the rest of the list xs
  • create a new list of the transformed item, x', and the transformed rest of the list, xs'
    • x' :: xs'

It’s possible to pattern match directly in the function definition and avoid the intermediate values to make it less verbose, as in map'.