Signal a passing or failing grade if a condition is TRUE

pass_if() and fail_if() both create passing or failing grades if a given condition is TRUE. See graded() for more information on gradethis grade-signaling functions.

These functions are also used in legacy gradethis code, in particular in the superseded function grade_result(). While previous versions of gradethis allowed the condition to be determined by a function or formula, when used in grade_this() the condition must be a logical TRUE or FALSE.

Usage

pass_if(
  cond,
  message = NULL,
  ...,
  env = parent.frame(),
  praise = getOption("gradethis.pass.praise", FALSE),
  x = deprecated()
)

fail_if(
  cond,
  message = NULL,
  ...,
  env = parent.frame(),
  hint = getOption("gradethis.fail.hint", FALSE),
  encourage = getOption("gradethis.fail.encourage", FALSE),
  x = deprecated()
)

Arguments

cond: A logical value or an expression that will evaluate to a TRUE or FALSE value. If the value is TRUE, or would be considered TRUE in an if (cond) statement, then a passing or failing grade is returned to the user.
message: A character string of the message to be displayed. In all grading helper functions other than graded(), message is a template string that will be processed with glue::glue().
...: Passed to graded() in grade_this().
env: environment to evaluate the glue message. Most users of gradethis will not need to use this argument.
praise: Include a random praising phrase with random_praise()? The default value of praise can be set using gradethis_setup() or the gradethis.pass.praise option.
x: Deprecated. Replaced with cond.
hint: Include a code feedback hint with the failing message? This argument only applies to fail() and fail_if_equal() and the message is added using the default options of give_code_feedback() and maybe_code_feedback(). The default value of hint can be set using gradethis_setup() or the gradethis.fail.hint option.
encourage: Include a random encouraging phrase with random_encouragement()? The default value of encourage can be set using gradethis_setup() or the gradethis.fail.encourage option.

Value

pass_if() and fail_if() signal a correct or incorrect grade if the provided condition is TRUE.

Functions

pass_if: Pass if cond is TRUE.
fail_if: Fail if cond is TRUE.

Examples

# Suppose the prompt is to find landmasses in `islands` with land area of
# less than 20,000 square miles. (`islands` reports land mass in units of
# 10,000 sq. miles.)

grader <-
  # ```{r example-check}
  grade_this({
    fail_if(any(is.na(.result)), "You shouldn't have missing values.")

    diff_len <- length(.result) - length(.solution)
    fail_if(diff_len < 0, "You missed {abs(diff_len)} island(s).")
    fail_if(diff_len > 0, "You included {diff_len} too many islands.")

    pass_if(all(.result < 20), "Great work!")

    # Fall back grade
    fail()
  })
# ```

.solution <-
  # ```{r example-solution}
  islands[islands < 20]
# ```

# Peek at the right answer
.solution
#>     Axel Heiberg           Hainan           Kyushu         Melville 
#>               16               13               14               16 
#>      New Britain  Prince of Wales      Southampton      Spitsbergen 
#>               15               13               16               15 
#>           Taiwan Tierra del Fuego            Timor        Vancouver 
#>               14               19               13               12 

# Has missing values somehow
grader(mock_this_exercise(islands["foo"], !!.solution))
#> <gradethis_graded: [Incorrect] You shouldn't have missing values.>

# Has too many islands
grader(mock_this_exercise(islands[islands < 29], !!.solution))
#> <gradethis_graded: [Incorrect] You included 4 too many islands.>

# Has too few islands
grader(mock_this_exercise(islands[islands < 16], !!.solution))
#> <gradethis_graded: [Incorrect] You missed 4 island(s).>

# Just right!
grader(mock_this_exercise(islands[islands < 20], !!.solution))
#> <gradethis_graded: [Correct] Great work!>