Chapter 9 - Teach Yourself Scheme in Fixnum Days[Go to...

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Teach Yourself Scheme in Fixnum Days [Go to first , previous , next page; contents ; index ] Chapter 9 Structures Data that are naturally grouped are called structures . One can use Scheme's compound data types, eg, vectors or lists, to represent structures. Eg, let's say we are dealing with grouped data relevant to a (botanical) tree . The individual elements of the data, or fields , could be: height , girth , age , leaf-shape , and leaf-color , making a total of 5 fields. Such data could be represented as a 5-element vector. The fields could be accessed using vector-ref and modified using vector-set! . Nevertheless, we wouldn't want to be saddled with the burden of remembering which vector index corresponds to which field. That would be a thankless and error-prone activity, especially if fields get excluded or included over the course of time. We will therefore use a Scheme macro defstruct to define a structure data type, which is basically a vector, but which comes with an appropriate suite of procedures for creating instances of the structure, and for accessing and modifying its fields. Thus, our tree
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