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_quosures(x, env = caller_env())

parse_expr(x)

parse_exprs(x)

Arguments

x

Text containing expressions to parse_expr for parse_expr() and parse_exprs(). Can also be an R connection, for instance to a file. If the supplied connection is not open, it will be automatically closed and destroyed.

env

The environment for the quosures. Depending on the use case, a good default might be the global environment but you might also want to evaluate the R code in an isolated context (perhaps a child of the global environment or of the base environment).

Value

parse_expr() returns an expression, parse_exprs() returns a list of expressions.

Details

parse_expr() returns one expression. If the text contains more than one expression (separated by semicolons 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 suffixed with _quo and quos return quosures rather than raw expressions.

Life cycle

  • parse_quosure() and parse_quosures() were soft-deprecated in rlang 0.2.0 and renamed to parse_quo() and parse_quos(). This is consistent with the rule that abbreviated suffixes indicate the return type of a function.

See also

base::parse()

Examples

# parse_expr() can parse any R expression: parse_expr("mtcars %>% dplyr::mutate(cyl_prime = cyl / sd(cyl))")
#> 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)")
#> [[1]] #> NULL #> #> [[2]] #> list() #> #> [[3]] #> foo(bar) #>
# 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))
#> [[1]] #> [1] 1 #> #> [[2]] #> [1] 2 #> #> [[3]] #> mtcars #>