CODEWITHSUNDEEP
clojure
SamPeng
SamPeng

Reputation: 38

clojure list operation result not equal

I test some list operation, find this difference with two syntax。

(conj (cons 321321 [1]) 123123123)
=> (123123123 321321 1)

and

(cons 321321 [1])
=> (321321 1)
(conj [321312 1] 123123123)
=> [321312 1 123123123]

why these result isn't equal?

Upvotes: 0

Views: 84

Answers (1)

cfrick
cfrick

Reputation: 37073

Because you are doing different things.

cons http://clojuredocs.org/clojure.core/cons

Returns a new seq where x is the first element and seq is the rest.

conj http://clojuredocs.org/clojure.core/conj

Returns a new collection with the xs 'added'. (conj nil item) returns (item). The 'addition' may happen at different 'places' depending on the concrete type.

in your first example you are "prepending" a new entry (easiest way for conj to add to a sequence) and in your second example you are "appending" to a vector (again easiest way for conj to add).

user=> (.getClass (cons 321321 [1]))
clojure.lang.Cons
user=> (.getClass (conj (cons 321321 [1]) 123123123))
clojure.lang.Cons

Note you are using [...] next!

user=> (.getClass [321312 1])
clojure.lang.PersistentVector
user=> (.getClass (conj [321312 1] 123123123))
clojure.lang.PersistentVector

Upvotes: 8

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