The behavior we require to implement
a pair is that it glues two values together. Stated as a behavior condition,
- If a pair p was constructed from values x and y , then select(p, 0) returns x , and select(p, 1) returns y .
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2.2 Data Abstractionew can be applied broadly, including to the pair values
that we used to implement rational numbers. We never actually said much about
what a pair was, only that the language supplied the means to create and
manipulate lists with two elements. <span>The behavior we require to implement
a pair is that it glues two values together. Stated as a behavior condition,
If a pair p was constructed from values x and y , then
select(p, 0) returns x , and select(p, 1) returns
y .
We don't actually need the list type to create pairs. Instead, we can
implement two functions pair and select that fulfill this description
just as well as a two-element list.
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