Dylan Design Notes

#10: Element-Setter Signals Error	(Clarification)

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

It is an error if element-setter cannot successfully set the element 
of a sequence.  This design note requires an error to be signaled in 
that case, preventing programs from silently returning an incorrect 
result or otherwise failing.

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Specify that if element-setter cannot successfully set the element of 
a sequence, it should signal an error.  The second paragraph of the 
description of element-setter on page 127 of the Dylan manual should 
be changed to read, "An error is signaled if a program calls element-
setter with a key that is not already a key to collection, unless the 
collection supports the dynamic addition of keys and adds the key and 
new-value."

