Problem Statement

Given a string and defined variables or values, string interpolation is the replacement of defined character sequences in the string by values or variable values.

Note: The task is not to create a string interpolation routine, but to show a language's built-in capability.

Let's start with the solution:

;; format uses %a or ~a as replacement directive
(format "Mary had a ~a lamb" "little")
   → "Mary had a little lamb"
(format "Mary had a %a lamb" "little")
   → "Mary had a little lamb"