Evaluate code in qenv

Evaluate code in qenv

Usage

eval_code(object, code)

# S3 method for class 'qenv'
within(data, expr, ...)

Arguments

object: (qenv)
code: (character, language or expression) code to evaluate. It is possible to preserve original formatting of the code by providing a character or an expression being a result of parse(keep.source = TRUE).
data: (qenv)
expr: (expression) to evaluate. Must be inline code, see Using language objects...
...: named argument value will substitute a symbol in the expr matched by the name. For practical usage see Examples section below.

Value

qenv environment with code/expr evaluated or qenv.error if evaluation fails.

Details

eval_code() evaluates given code in the qenv environment and appends it to the code slot. Thus, if the qenv had been instantiated empty, contents of the environment are always a result of the stored code.

within() is a convenience method that wraps eval_code to provide a simplified way of passing expression. within accepts only inline expressions (both simple and compound) and allows to substitute expr with ... named argument values.

Using language objects with `within`

Passing language objects to expr is generally not intended but can be achieved with do.call. Only single expressions will work and substitution is not available. See examples.

Examples

# evaluate code in qenv
q <- qenv()
q <- eval_code(q, "a <- 1")
q <- eval_code(q, "b <- 2L # with comment")
q <- eval_code(q, quote(library(checkmate)))
q <- eval_code(q, expression(assert_number(a)))

# evaluate code using within
q <- qenv()
q <- within(q, {
  i <- iris
})
q <- within(q, {
  m <- mtcars
  f <- faithful
})
q
#> <environment: 0x5577d2175498> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - f: [data.frame]
#> - i: [data.frame]
#> - m: [data.frame]
get_code(q)
#> [1] "i <- iris\nm <- mtcars\nf <- faithful"

# inject values into code
q <- qenv()
q <- within(q, i <- iris)
within(q, print(dim(subset(i, Species == "virginica"))))
#> [1] 50  5
#> <environment: 0x5577d2a97128> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - i: [data.frame]
within(q, print(dim(subset(i, Species == species)))) # fails
#> <qenv.error: object 'species' not found 
#>  when evaluating qenv code:
#> print(dim(subset(i, Species == species)))>
within(q, print(dim(subset(i, Species == species))), species = "versicolor")
#> [1] 50  5
#> <environment: 0x5577cfa3b5a8> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - i: [data.frame]
species_external <- "versicolor"
within(q, print(dim(subset(i, Species == species))), species = species_external)
#> [1] 50  5
#> <environment: 0x5577ce13d8d0> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - i: [data.frame]

# pass language objects
expr <- expression(i <- iris, m <- mtcars)
within(q, expr) # fails
#> <qenv.error: object 'expr' not found 
#>  when evaluating qenv code:
#> expr>
do.call(within, list(q, expr))
#> <environment: 0x5577d17d2158> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - i: [data.frame]
#> - m: [data.frame]

exprlist <- list(expression(i <- iris), expression(m <- mtcars))
within(q, exprlist) # fails
#> <qenv.error: object 'exprlist' not found 
#>  when evaluating qenv code:
#> exprlist>
do.call(within, list(q, do.call(c, exprlist)))
#> <environment: 0x5577d1f90f60> 🔒 
#> Parent: <environment: package:checkmate> 
#> Bindings:
#> - i: [data.frame]
#> - m: [data.frame]