# CustomAnswerCheckers

## Custom Answer Checkers: PG Code Snippet

*This code snippet shows the essential PG code to write problems that check "arbitrary" conditions on the student's answer. Note that these are insertions, not a complete PG file. This code will have to be incorporated into the problem file on which you are working.*

Note that it is possible to do this with old-style answer checkers as well. However, it's more straightforward to do it with MathObjects based answer checkers, so that's the method that we use here.

PG problem file | Explanation |
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$ans = pi/3; $val = cos($ans); |
To set up the custom answer checker we will override the answer checker routine for the MathObject that we're using to check the answer. Thus our answer object should be of the same type (e.g., Real, Formula, etc.) as what we want the student to be entering. For example, here we're going to ask for a value of
In this sample, we've taken advantage of a bunch of overloading that MathObjects do: the line
Similarly, |

BEGIN_TEXT Enter a value of \(x\) for which \(\cos(x) = $val\): \(x = \) \{ ans_rule(25) \} END_TEXT |
We don't have to make any changes or additions to the text section of the file. |

ANS( $ans->cmp( checker=>sub { my ( $correct, $student, $ansHash ) = @_; return cos($correct) == cos($student); } ) ); |
Then when setting up the answer and solution section, we overwride the default answer checker in the answer. The replacement is a Perl subroutine that takes as its arguments the correct answer, student answer, and answer hash that is being processed in the answer comparison. Its return value should be 1 if the student's answer is correct, and 0 (false) otherwise. We could also specify the answer checker as a separate subroutine by writing sub mycheck { my ($correct, $student, $ansHash) = @_; return cos($student) == cos($correct); } ANS( $ans->cmp( checker=>~~&mycheck ) ); (The
One final point: we can set an error message in the answer checker by using sub mycheck { my ($correct, $student, $ansHash) = @_; Value->Error("Try again") if cos($student)==sqrt(3)/2; return cos($student) == cos($correct); } ANS( $ans->cmp( checker=>~~&mycheck ) ); |