These functions check whether the argument x is a single
atomic value of type numeric, integer or
character.
If x does have the required length and type, the result
of the function is the logical value TRUE.
Otherwise, if fatal=TRUE (the default) an error occurs,
while if fatal=FALSE a warning is issued (if warn=TRUE)
and the function returns the value FALSE.
x <- pi check.1.real(x)
check.1.integer(pi, fatal=FALSE, context="In your dreams,")
check.1.string(x, fatal=FALSE)
check.1.integer(x, fatal=FALSE, warn=FALSE)