CODEWITHSUNDEEP
clojurefunctional-programmingcurryingclojure-core
NeuronQ
NeuronQ

Reputation: 8195

What does calling map with one argument do in Clojure?

In Clojure, what does calling map with one argument, like this:

(map inc) ;=> #object[clojure.core$map$fn__4549 0x1decdb9d "clojure.core$map$fn__4549@1decdb9d"]

...do / return? Because it doesn't do auto currying as expected, so the following two expressions are not equivalent:

;; E1
((map inc) [100 200 300]) ;=> #object[clojure.core$map$fn__4549$fn__4550 0x1b0c8974 "clojure.core$map$fn__4549$fn__4550@1b0c8974"]

;; E2
((partial map inc) [100 200 300]) ;=> (101 201 301)

...and the documentation says nothing.

So what IS the mysterious function returned by (map inc) and other similar expressions?

Upvotes: 2

Views: 185

Answers (1)

Arthur Ulfeldt
Arthur Ulfeldt

Reputation: 91534

calling map with a single argument in clojure 1.7+ returns a transducer that can be composed with other transducers and eventually a call to into or some other transducing thing.

I recommend this video first, and then this one

This allows you to use all the clojure sequence abstractions without the computer spending a lot of time building intermediate sequences.

In clojure less than 1.7 it will throw an arity exception

Upvotes: 4

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