x is a
call, or an
object to be tested.
name is also known as ‘symbol’, from its type
typeof(x) == "language", then
is always true, but the reverse does not hold as expressions or
y also fulfill
is.language(y), see the examples.
This is a primitive function.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
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))
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