Armed with an understanding of (1) the core computational model in Lisp— λ-calculus; (2) the recursive specifications of data structures and recursive definitions of algorithms; and (3) the representation of lists in memory, we are prepared to develop functions that operate on data structures.
5.6.1 A List length Function
Consider the following function length1,8 which given a list, returns the length of the list:
The built-in Scheme predicate null? returns true if its argument is an empty list and false otherwise. The built-in Scheme predicate empty? can be used for this purpose as well.
Notice that the ...
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