| parse_expr {rlang} | R Documentation |
These functions parse and transform text into R expressions. This is the first step to interpret or evaluate a piece of R code written by a programmer.
parse_expr(x) parse_exprs(x) parse_quosure(x, env = caller_env()) parse_quosures(x, env = caller_env())
x |
Text containing expressions to parse_expr for
|
env |
The environment for the formulas. Defaults to the
context in which the parse_expr function was called. Can be any
object with a |
parse_expr() returns one expression. If the text contains more
than one expression (separated by colons or new lines), an error is
issued. On the other hand parse_exprs() can handle multiple
expressions. It always returns a list of expressions (compare to
base::parse() which returns an base::expression vector). All
functions also support R connections.
The versions prefixed with f_ return expressions quoted in
formulas rather than raw expressions.
parse_expr() returns a formula, parse_exprs() returns a
list of formulas.
# parse_expr() can parse_expr any R expression:
parse_expr("mtcars %>% dplyr::mutate(cyl_prime = cyl / sd(cyl))")
# A string can contain several expressions separated by ; or \n
parse_exprs("NULL; list()\n foo(bar)")
# The versions suffixed with _f return formulas:
parse_quosure("foo %>% bar()")
parse_quosures("1; 2; mtcars")
# The env argument is passed to as_env(). It can be e.g. a string
# representing a scoped package environment:
parse_quosure("identity(letters)", env = empty_env())
parse_quosures("identity(letters); mtcars", env = "base")
# You can also parse source files by passing a R connection. Let's
# create a file containing R code:
path <- tempfile("my-file.R")
cat("1; 2; mtcars", file = path)
# We can now parse it by supplying a connection:
parse_exprs(file(path))