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Unevaluated Expressions

Usage

expression(...)

is.expression(expr)
as.expression(expr)

Value

An ``expression'' object containing its unevaluated arguments. Expression objects conceptually are lists of ``calls'' and so the subsetting operations which apply to lists also apply to them. For compatibility with S, the mode function will return "expression" for expression objects.

is.expression returns TRUE if expr is an expression object and FALSE otherwise.

as.expression attempts to coerce its argument into an expression object.

See Also

call, eval, function. Further,text and legend for plotting math expressions.

Examples

length(ex1 <- expression(1+ 0:9))# 1
ex1
eval(ex1)# 1:10

length(ex3 <- expression(u,v, 1+ 0:9))# 3
mode(ex3 [3]) # expression
mode(ex3[[3]])# call
rm(ex3)