[plt-scheme] srfi 1 impl: delete-duplicates!, append! - bugs?

Jacob Matthews escribió:
> Igor Mikhailov wrote:
> 
>> I can not understand, is these bugs or features?
> 
> Features. The append! and delete-duplicates! functions still _return_ 
> the relevant result rather than mutating their argument into that result 
> --- the difference between the ! versions and the non-! versions is that 
> the ! versions are allowed to mutate their arguments however they'd like 
> in the process (presumably to make them faster or more memory-efficient).
> 

Thank you very much.
I have missed that key word is _allowed_ to mutate, not _required_ to 
mutate.

Igor.