Is object a node or pairlist?

Description

• 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

See Also

is_lang() tests for language nodes.