Check whether a student correctly called a function/operator

Check whether a student called a function correctly. Note: test_function and test_function_v2 are now identical and either can be used.

check_function(state, name, index = 1, not_called_msg = NULL,
  append = TRUE)

check_operator(state, name, index = 1, append = TRUE,
  not_called_msg = NULL)

check_arg(state, arg, arg_not_specified_msg = NULL, append = TRUE)

# S3 method for ArgumentState
check_equal(state, incorrect_msg = NULL,
  eval = TRUE, eq_condition = "equivalent", eq_fun = NULL,
  append = TRUE, ...)

Arguments

state	state to start from
name	name of the function/operator as a string, e.g. "mean" or "+"
index	integer that specifies which call of name in the solution code will be checked.
not_called_msg	custom feedback message in case the student did not call the function often enough.
append	Whether or not to append the feedback to feedback built in previous states
arg	name or position of argument to specify ... Arguments can be accessed using '..<INDEX>' (see example 5) (for check_arg)
arg_not_specified_msg	custom message in case argument was not specified (for check_arg)
incorrect_msg	custom feedback message in case the student did not call the function with the same argument values as in the sample solution. You can specify a vector of arguments with the same length as args, to have argument-specific custom feedback.
eval	logical vector indicating whether and how to compare arguments. If eval is NA, student and solution argument are not compared. If eval is FALSE, the string versions of the arguments are compared. If eval is TRUE, the argument in the student code is evaluated in the student environment and the argument in the solution code is evaluated in the solution environment, and their results are compared. Setting this to FALSE can be useful, e.g., to check whether the student supplied a large predefined object, or when you're in a sub-SCT where the environments are not unambiguously available.
eq_condition	character vector indicating how to perform the comparison for each argument. See is_equal.
eq_fun	optional argument to specify a custom equality function. The function should take two arguments and always return a single boolean value: TRUE or FALSE.
...	S3 stuff

Examples

if (FALSE) {
# Example 1
mean(1:3)

# SCT
ex() %>% check_function("mean") %>% check_arg("x") %>% check_equal()

# Example 2
mean(c(NA, 1, 2), na.rm = TRUE)

# SCT
ex() %>% check_function("mean") %>% {
  check_arg(., "x") %>% check_equal()
  check_arg(., "na.rm") %>% check_equal()
}

# Example 3
5 + 4

# SCT
ex() %>% check_operator("+") %>% check_result() %>% check_equal()

# Example 4: Positional argument check
cor(rnorm(10), rnorm(10))

# SCT
ex() %>% check_function("cor") %>% {
  check_arg(., 1) %>% check_equal()
  check_arg(., 2) %>% check_equal()
}

# Example 5: ... in check_args

soln <- "std_dev <- purrr::compose(sqrt, var, .dir='forward')"
state <- setup_state(soln, soln)
state %>% check_function(., "compose") %>% {
  check_arg(., '..1') %>% check_equal() # sqrt
  check_arg(., '..2') %>% check_equal() # var
  check_arg(., '.dir') %>% check_equal()
}

}