Implement a syntactic transformation

Let expressions are derived expressions, because

(let ((var1 exp1) ... (varn expn))
  body)

is equivalent to

((lambda (var1 ... varn)
   body)
 exp1
 ...
 expn)

Implement a syntactic transformation let->combination that reduces evaluating let expressions to evaluating combinations of the type shown above, and add the appropriate clause to eval to handle let expressions.

Nobody's finished this exercise yet. You'll be the first!