Generic pattern:

   (apply reducer
          (map item-function
               list-of-values))










Session 6:

   (apply string 
          (map first-char
               list-of-strings))











There are many variations:

  - map a built-in function
    or: one we write

  - apply a built-in function
    or:   one we write





Generic pattern:

   (apply reducer
          (map item-function
               (preprocess list-of-values))))





Generic pattern:

   (apply reducer
          (map item-function
               (filter item-test
                       (preprocess list-of-values))))