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Exercise 3.5
A list replication function **

Write a tail recursive function called replicate-to-length, which in a cyclic way (if necessary) replicates the elements in a list until the resulting list is of certain exact length. The following serves as an example:

        (replicate-to-length '(a b c) 8) =>
        (a b c a b c a b)
        (replicate-to-length '(a b c) 2) =>
        (a b)

In other words, in (replicate-to-length lst n), take elements out of lst, cyclically if necessary, until you reach n elements.