is.language               package:base               R Documentation

Is an Object a Language Object?

Description:

     'is.language' returns 'TRUE' if 'x' is either a variable 'name', a
     'call', or an 'expression'.

Usage:

     is.language(x)

Arguments:

       x: object to be tested.

Details:

     'is.language' is generic: you can write methods to handle specific
     classes of objects, see InternalMethods.

References:

     Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) _The New S
     Language_. Wadsworth & Brooks/Cole.

Examples:

     ll <- list(a = expression(x^2 - 2*x + 1), b = as.name("Jim"),
                c = as.expression(exp(1)), d = call("sin", pi))
     sapply(ll, typeof)
     sapply(ll, mode)
     stopifnot(sapply(ll, is.language))

