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23 lines
749 B
23 lines
749 B
2 years ago
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Exercise 4.7: Let* is similar to
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let, except that the bindings of the let* variables are performed
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sequentially from left to right, and each binding is made in an environment in
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which all of the preceding bindings are visible. For example
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(let* ((x 3)
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(y (+ x 2))
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(z (+ x y 5)))
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(* x z))
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returns 39. Explain how a let* expression can be rewritten as a set of
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nested let expressions, and write a procedure let*->nested-lets
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that performs this transformation. If we have already implemented let
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(Exercise 4.6) and we want to extend the evaluator to handle let*,
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is it sufficient to add a clause to eval whose action is
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(eval (let*->nested-lets exp) env)
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or must we explicitly expand let* in terms of non-derived expressions?
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