The call type(x, 'uneval') checks to see if x is of type uneval.  It returns true if x is of type uneval, and false otherwise.

Expressions of type uneval are produced by enclosing an expression in right single quotes ('). This is used to delay the evaluation of the quoted expression. For more information on unevaluated expressions, see ?uneval.

Note that in a call type('s', 'uneval'), the quoted first argument  is first evaluated before being passed to type, so that the procedure type ``sees'' the unquoted expression s, not the quoted expression . This is equally true of the (quoted) type name 'uneval' that, when evaluated, results in the name uneval being passed to type.

When used as a procedure parameter modifier, uneval declares that an argument to a procedure is automatically left unevaluated.