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\name{verbalogic}
\alias{verbalogic}
\title{
Verbal Logic
}
\description{
Perform the specified logical operation
on the character vector \code{x}, recognising the
special strings \code{"TRUE"} and \code{"FALSE"}
and treating other strings as logical variables.
}
\usage{
verbalogic(x, op = "and")
}
\arguments{
\item{x}{
Character vector.
}
\item{op}{
Logical operation: one of the character strings
\code{"and"}, \code{"or"} or \code{"not"}.
}
}
\details{
This function performs simple logical operations
on character strings that represent human-readable statements.
The character vector \code{x} may contain any strings:
the special strings \code{"TRUE"} and \code{"FALSE"} are
treated as the logical values \code{TRUE} and \code{FALSE},
while all other strings are treated as if they were
logical variables.
If \code{op="and"}, the result is a single string,
logically equivalent to \code{x[1] && x[2] && ... && x[n]}.
First, any entries of \code{x} equal to \code{"TRUE"} are removed.
The result is \code{"FALSE"} if any of the entries of \code{x}
is \code{"FALSE"}; otherwise it is equivalent to
\code{paste(x, collapse=" and ")}.
If \code{op="or"}, the result is a single string, logically equivalent to
\code{x[1] || x[2] || ... || x[n]}.
First, any entries of \code{x} equal to \code{"FALSE"} are removed.
The result is \code{"TRUE"} if any of the entries of \code{x}
is \code{"TRUE"}; otherwise it is equivalent to
\code{paste(x, collapse=" or ")}.
If \code{op="not"}, the result is a character vector \code{y}
such that \code{y[i]} is the logical negation of \code{x[i]}.
The code does not understand English grammar and cannot expand logical
expressions.
}
\value{
A character string.
}
\author{
\adrian.
}
\examples{
x <- c("The sky is blue", "my name is not Einstein", "FALSE")
verbalogic(x, "and")
verbalogic(x, "or")
verbalogic(x, "not")
}
\keyword{logic}
\keyword{manip}
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