Debug an exercise submission

When used in a *-check chunk or inside grade_this(), debug_this() displays in the learnr tutorial a complete listing of the variables and environment available for checking. This can be helpful when you need to debug an exercise and a submission.

debug_this(check_env = parent.frame())

Arguments

check_env	A grade checking environment. You can use mock_this_exercise() to prepare a mocked exercise submission environment. Otherwise, you don't need to use or set this argument.

Value

Returns a neutral grade containing a message that includes any and all information available about the exercise and the current submission. The output lets you visually explore the objects available for use within your grade_this() grading code.

Debugging exercises

debug_this() gives you a few ways to see the objects that are available inside grade_this() for you to use when grading exercise submissions. Suppose we have this example exercise:

```{r example-setup}
x <- 1
```

```{r example, exercise = TRUE}
# user submits
y <- 2
x + y
```

```{r example-solution}
x + 3
```

The debug output will look like the following when used as described below.

Exercise label (.label): example
Engine (.engine): r

Submission (.result, .user, .last_value):

[1] 3

Solution (.solution):

[1] 4

.envir_prep

 $ x: num 1

.envir_result

 $ x: num 1

.user_code

# user submits
x + 2

.solution_code

x + 3

Always debug

The first method is the most straight-forward. Inside the *-check or *-error-check chunks for your exercise, simply call debug_this():

```{r example-check}
debug_this()
```

Every time you submit code for feedback via Submit Answer, the debug information will be printed.

Debug specific cases

On the other hand, if you want to debug a specific submission, such as a case where a submission isn't matching any of your current grading conditions, you can call debug_this() wherever you like inside grade_this().

```{r example-check}
grade_this({
  pass_if_equal(3, "Good work?")
  
  # debug the submission if it is somehow equal to 2
  if (.result == 2) {
    debug_this()
  }
})
```

Debug default fail condition

It's common to have the grade-checking code default to an incorrect grade with code feedback by calling fail() at the end of the checking code in grade_this(). During development of a tutorial, you may want to have this default fail() return the debugging information rather than a failure.

By setting the global option gradethis.fail to use debug_this(),

```{r setup}
library(learnr)
library(gradethis)
gradethis_setup()

option(gradethis.fail = "{debug_this()}")
```

you can see the values that are available to you during the submission check whenever your test submissions pass through your other checks.

```{r example-check}
grade_this({
  pass_if_equal(3, "Good work?")
  
  fail()
})
```

Don't forget to reset or unset the gradethis.fail option when you're done working on your tutorial.

Examples

# Suppose we have an exercise (guess the number 42). Mock a submission:
submission <- mock_this_exercise(.user_code = 40, .solution_code = 11 + 31)

# Call `debug_this()` inside your *-check chunk, is equivalent to
debug_this()(submission)$message
#> <p>
#>   <strong>Exercise label (<code>.label</code>):</strong>
#>   <code>mock</code>
#>   <br/>
#>   <strong>Engine (<code>.engine</code>):</strong>
#>   <code>r</code>
#> </p>
#> <p>
#>   Submission (<code>.result</code>, <code>.user</code>, <code>.last_value</code>):
#>   <pre class="r"><code>[1] 40</code></pre>
#> </p>
#> <p>
#>   Solution (<code>.solution</code>):
#>   <pre class="r"><code>[1] 42</code></pre>
#> </p>
#> <details>
#>   <summary>
#>     <code>.envir_prep</code>
#>   </summary>
#>   <pre><code></code></pre>
#> </details>
#> <details>
#>   <summary>
#>     <code>.envir_result</code>
#>   </summary>
#>   <pre><code></code></pre>
#> </details>
#> <details>
#>   <summary>
#>     <code>.user_code</code>
#>   </summary>
#>   <pre class="r"><code>40</code></pre>
#> </details>
#> <details>
#>   <summary>
#>     <code>.solution_code</code>
#>   </summary>
#>   <pre class="r"><code>11 + 31</code></pre>
#> </details>

# The remaining examples produce equivalent output
if (FALSE) {
  # Or you can call `debug_this()` inside a `grade_this()` call
  # at the point where you want to get debug feedback.
  grade_this({
    pass_if_equal(42, "Good stuff!")
  
    # Find out why this is failing??
    debug_this()
  })(submission)
  
  # Set default `fail()` message to show debug information
  # (for tutorial development only!)
  old_opts <- options(gradethis.fail = "{debug_this()}")
  
  grade_this({
    pass_if_equal(42, "Good stuff!")
  
    fail()
  })(submission)
  
  # default fail() will show debug until you reset gradethis.fail option
  options(old_opts)
}