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Author: dpvc
Date: Tue Mar 29 03:25:29 2005 UTC (14 years, 7 months ago)
Log Message:
Compartmentalize the equality check one step further.  The cmp_equal
method now calls a new cmp_compare method to perform the actual
comparison (rather than use == directly).  The cmp_compare method
either calls a user-supplied checker routine, or defaults to using the
== operator.  The list checker also uses cmp_compare to check the
individual items in the list.  The list checker also calls a new
cmp_list_checker method to perform the list check.  This can be
overridden by a user-supplied list-checking routine.

To supply an alternate checking routine, use the "checker" option to
the cmp() method of the correct answer object.  For example:

    sub check {
      my ($correct,$student,$ans) = @_;
      return 0 unless $correct->length == $student->length;
      my ($x,$y) = $student->value;  # break up a point;
      return $x**2 - $y**2 = 1;      # check if it is on a hyperbola
    }
    Point(1,0)->cmp(checker=>~~&check);

This will check if the student's point lies on the given hyperbola.  All
the usual error messages will be issued if the student's answer is not
a point, or is of the wrong dimension, etc.

You can use

    sub list_check {
      my ($correct,$student,$ans) = @_;
      my @correct = @{$correct}; my @student = @{$student};
      ...
      return ($score,@errors);
    }
    List(...)->cmp(list_checker=>~~&list_check);

to replace the list-checking routine with your own custom one.  The
$correct and $student values are array references to the elements in
the lists provided by the professor and student.  (Note that you do
NOT get a List() object; this allows you to handle lists of formulas,
since a List of formulas becomes a formula returning a list).  The
checker routine should return the number of correct elements in the
student's list ($score), and a list of error messages produced while
checking the two lists (@errors).  (This is a list of messages, since
you might want to include an error for each entry in the list, for
example).

If your checker or list_checker routine wants to die with an error
message, use Value::Error(message).  This will put the message in the
WeBWorK display area at the top of the page.  If you use die(message),
or if the code fails due to a runtime error, then "pink screen of
death" will be produced indicating the error and asking the student to
report the error to the professor.

Changed paths:

Path Details
Directorytrunk/pg/lib/Value/AnswerChecker.pm modified , text changed

aubreyja at gmail dot com
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