# is_pairlist

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##### Is object a node or pairlist?

• is_pairlist() checks that x has type pairlist or NULL. NULL is treated as a pairlist because it is the terminating node of pairlists and an empty pairlist is thus the NULL object itself.

• is_node() checks that x has type pairlist.

In other words, is_pairlist() tests for the data structure while is_node() tests for the internal type.

##### Usage
is_pairlist(x)is_node(x)
##### Arguments
x

Object to test.

is_lang() tests for language nodes.