R: Examples for 'rlang::expr'

### ** Examples

# R normally returns the result of an expression
1 + 1

[1] 2

# `expr()` defuses the expression that you have supplied and
# returns it instead of its value
expr(1 + 1)

1 + 1

expr(toupper(letters))

toupper(letters)

# It supports _injection_ with `!!` and `!!!`. This is a convenient
# way of modifying part of an expression by injecting other
# objects.
var <- "cyl"
expr(with(mtcars, mean(!!sym(var))))

with(mtcars, mean(cyl))

vars <- c("cyl", "am")
expr(with(mtcars, c(!!!syms(vars))))

with(mtcars, c(cyl, am))

# Compare to the normal way of building expressions
call("with", call("mean", sym(var)))

with(mean(cyl))

call("with", call2("c", !!!syms(vars)))

with(c(cyl, am))

Examples for 'rlang::expr'

Defuse an R expression