|Parameters||l, a list|
i, an integer
|Purpose||Extracts the ith element of the list. Elements are numbered starting at 0.|
|Produces||An element of the list.|
|Preconditions||Two parameters (verified).|
l is a list (verified). i >= 0 (verified). i <
|Postconditions||Does not affect l.|
> (list-ref (list 1 2 3) 0) 1 > (list-ref (list 'a 'b 'c) 0) a > (list-ref (list 'a 'b 'c) 2) c > (list-ref (list 'a 'b 'c) 3) list-ref: index 3 too large for list: (a b c) > (define lists (list (list 'a 'b 'c) (list 1) (list 4 2 1 0))) > lists ((a b c) (1) (4 2 1 0)) > (list-ref lists 0) (a b c) > (list-ref (list-ref lists 0) 1) b > (list-ref (list 'a 'b 'c) -1) list-ref: expects type <non-negative exact integer> as 2nd argument, given: -1; other arguments were: (a b c)
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