Dmitri wrote:
> I notice that certain sequence operations such as concat and cons will
> not retain the original type of sequence, for example if you combine
> two vectors together a list will be returned:
>
> user=> (concat [1 2] [3 4])
> (1 2 3 4)
>
> is this intentional behavior, and would it not be more consistent for
> concat to retain the original type of the data structures, when both
> data structures that were passed in are of the same type.
It's because concat returns a lazy sequence, the concatenation only
happens when you ask for relevant elements (which has the benefit that
it doesn't need to do any copying, saving both time and memory). If you
want to concatenate two vectors eagerly (so returning another vector)
you could use 'into' instead:
user=> (into [1 2] [3 4])
[1 2 3 4]
> Also, why
> does cons behave differently from conj:
>
> user=> (conj [1 2] 3)
> [1 2 3]
>
> user=> (cons 2 [1 2])
> (2 1 2)
Because cons always creates a list (which construct at the front), while
conj "adds" it in the natural (ie fastest) way for that collection type,
vectors "add" at the end.
user> (conj '(1 2) 3)
(3 1 2)
user> (conj [1 2] 3)
[1 2 3]
user> (conj #{1 2} 3)
#{1 2 3}
user> (cons 3 '(1 2))
(3 1 2)
--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
-~----------~----~----~----~------~----~------~--~---
