Dylan Design Notes: #28: First, Second, Third are Functions (Change)

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Dylan Design Notes

Dylan Design Notes: #28: First, Second, Third are Functions (Change)
#28: First, Second, Third are Functions (Change)

Version 1, January 1994
Copyright (c) 1993-1994, Apple Computer

The functions first, second, third, and their associated setter functions are specified as generic functions on sequences. This design note changes them to functions.

Change the following functions currently documented as generic functions to instead be functions with the indicated definitions:

first sequence #key default => value
second sequence #key default => value
third sequence #key default => value

Each of these functions returns the indicated element of the sequence, by calling element with the supplied arguments and the corresponding index.

first-setter sequence new-value => new-value
second-setter sequence new-value => new-value
third-setter sequence new-value => new-value

Each of these functions sets the indicated element of the sequence and returns the new value, by calling element-setter with the supplied arguments and the corresponding index.

Notes

The functions first, second, third, and their associated setter functions are specified as generic functions on sequences. It would be a serious problem if any of them should differ from a call to element or element-setter (as appropriate) with the corresponding integer key. The existence of these functions without any specified methods makes it difficult for programmers to know whether they need to explicitly define additional methods for these functions that are applicable to new sequence classes.

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