Checks whether x is dereferencible. On JVM it checks if it is
an instance of clojure.lang.IDeref, on other platforms it may
be implemented in a similar or a completely different way.

Creates an identity reducible function from the collection c.

Checks whether x is an instance of the CollReduce protocol.

Establishes the monadic context that can be accessed
with the get-context function in the dynamic scope inside
the body.