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48 lines
1.2 KiB
48 lines
1.2 KiB
2 years ago
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Exercise 2.20: The procedures +,
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*, and list take arbitrary numbers of arguments. One way to
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define such procedures is to use define with
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dotted-tail notation.
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In a procedure definition, a parameter list that has a dot before
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the last parameter name indicates that, when the procedure is called, the
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initial parameters (if any) will have as values the initial arguments, as
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usual, but the final parameter’s value will be a
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list of any
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remaining arguments. For instance, given the definition
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(define (f x y . z) ⟨body⟩)
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the procedure f can be called with two or more arguments. If we
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evaluate
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(f 1 2 3 4 5 6)
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then in the body of f, x will be 1, y will be 2, and
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z will be the list (3 4 5 6). Given the definition
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(define (g . w) ⟨body⟩)
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the procedure g can be called with zero or more arguments. If we
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evaluate
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(g 1 2 3 4 5 6)
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then in the body of g, w will be the list (1 2 3 4 5
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6).77
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Use this notation to write a procedure same-parity that takes one or
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more integers and returns a list of all the arguments that have the same
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even-odd parity as the first argument. For example,
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(same-parity 1 2 3 4 5 6 7)
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(1 3 5 7)
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(same-parity 2 3 4 5 6 7)
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(2 4 6)
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