listp

listp( 
g_value 
) 
=> t / nil

Checks whether the specified object is a list.

The suffix p is usually added to the name of a function to indicate that it is a predicate function.

g_value

A data object.

`t`	If g_value is a list, a data type whose internal name is also `list`. `listp(nil)` returns `t`.
`nil`	The specified object is not a list.

listp('(1 2 3))  
=> t

listp( nil )     
=> t

listp( 1 )       
=> nil