AnswerHash.pm - a class to store student answers and the answer evaluator
This class stores information related to the student's answer. It is little more than a standard perl hash with a special name, but it does have some access and manipulation methods.
Usage:
$rh_ans = AnswerHash->new();The answer hash class is guaranteed to contain the following instance variables:
score => $correctQ,
correct_ans => $originalCorrEqn,
student_ans => $modified_student_ans
original_student_ans => $original_student_answer,
ans_message => $PGanswerMessage,
type => 'typeString',
preview_text_string => $preview_text_string,
preview_latex_string => $preview_latex_string
$ans_hash->{score} -- a number between 0 and 1 indicating
whether the answer is correct. Fractions
allow the implementation of partial
credit for incorrect answers.
$ans_hash->{correct_ans} -- The correct answer, as supplied by the
instructor and then formatted. This can
be viewed by the student after the answer date.
$ans_hash->{student_ans} -- This is the student answer, after reformatting;
for example the answer might be forced
to capital letters for comparison with
the instructors answer. For a numerical
answer, it gives the evaluated answer.
This is displayed in the section reporting
the results of checking the student answers.
$ans_hash->{original_student_ans} -- This is the original student answer.
This is displayed on the preview page and may be used for
sticky answers.
$ans_hash->{ans_message} -- Any error message, or hint provided by
the answer evaluator.
This is also displayed in the section reporting
the results of checking the student answers.
$ans_hash->{type} -- A string indicating the type of answer evaluator.
This helps in preprocessing the student answer for errors.
Some examples:
'number_with_units'
'function'
'frac_number'
'arith_number'
$ans_hash->{preview_text_string} --
This typically shows how the student answer was parsed. It is
displayed on the preview page. For a student answer of 2sin(3x)
this would be 2*sin(3*x). For string answers it is typically the
same as $ans_hash{student_ans}.
$ans_hash->{preview_latex_string} --
THIS IS OPTIONAL. This is latex version of the student answer
which is used to show a typeset view on the answer on the preview
page. For a student answer of 2/3, this would be \frac{2}{3}.
'ans_message' => '', # null string
'preview_text_string' => undef,
'preview_latex_string' => undef,
'error_flag' => undef,
'error_message' => '',Usage
$rh_anshash = AnswerHash->new;returns an object of type AnswerHash.
Usage:
$rh_ans->setKeys(score=>1, student_answer => "yes");Sets standard elements in the AnswerHash (the ones defined above). Will give error if one attempts to set non-standard key To set a non-standard element in a hash use
$rh_ans->{non-standard-key} = newValue;There are no safety checks when using this method.
Usage:
$rh_ans->data('foo'); # set $rh_ans->{student_ans} = 'foo';
$student_input = $rh_ans->data(); # retrieve value of $rh_ans->{student_ans}synonym for input
Usage:
$rh_ans->input('foo') # sets $rh_ans->{student_ans} = 'foo';
$student_input = $rh_ans->input();synonym for data
Usage: $rh_ans->score(1) $score = $rh_ans->score();
Retrieve or set $rh_ans->{score}, the student's score on the problem.
Usage:
$rh_ans->stringify_hash;Turns all values in the hash into strings (so they won't cause trouble outside the safe compartment). Hashes and arrays are converted into a JSON string.
Usage:
$rh_ans->throw_error("FLAG", "message");FLAG is a distinctive word that describes the type of error. Examples are EVAL for an evaluation error or "SYNTAX" for a syntax error. The entry $rh_ans->{error_flag} is set to "FLAG".
The catch_error and clear_error methods use this entry.
message is a descriptive message for the end user, defining what error occured.
Usage:
$rh_ans->catch_error("FLAG2");Returns true (1) if $rh_ans->{error_flag} equals "FLAG2", otherwise it returns false (empty string).
Usage:
$rh_ans->clear_error("FLAG2");If $rh_ans->{error_flag} equals "FLAG2" then the {error_flag} entry is set to the empty string as is the entry {error_message}
Usage:
$flag = $rh_ans -> error_flag();
$message = $rh_ans -> error_message();Retrieve or set the {error_flag} and {error_message} entries.
Use catch_error and throw_error where possible.
Usage:
$rh_ans->OR($rh_ans2);Returns a new AnswerHash whose score is the maximum of the scores in $rh_ans and $rh_ans2. The correct answers for the two hashes are combined with "OR". The types are concatenated with "OR" as well. Currently nothing is done with the error flags and messages.
Usage:
$rh_ans->AND($rh_ans2);Returns a new AnswerHash whose score is the minimum of the scores in $rh_ans and $rh_ans2. The correct answers for the two hashes are combined with "AND". The types are concatenated with "AND" as well. Currently nothing is done with the error flags and messages.
This class organizes the construction of answer evaluator subroutines which check the student's answer. By plugging filters into the answer evaluator class you can customize the way the student's answer is normalized and checked. Our hope is that with properly designed filters, it will be possible to reuse the filters in different combinations to obtain different answer evaluators, thus greatly reducing the programming and maintenance required for constructing answer evaluators.
Usage:
$ans_eval = new AnswerEvaluator;Create a new AnswerEvaluator
Usage:
AnswerEvaluator->new();Usage:
$answer_evaluator->evaluate($student_answer_string)Usage:
$answerHash->withPreFilter(filter[,options]);Installs a prefilter (possibly with options), and returns the AnswerHash. This is so that you can add a filter to a checker without having to save the checker in a variable, e.g.,
ANS(Real(10)->cmp->withPreFilter(...));or
ANS(num_cmp(10)->withPreFilter(...));Usage:
$answerHash->withPostFilter(filter[,options]);Installs a postfilter (possibly with options), and returns the AnswerHash. This is so that you can add a filter to a checker without having to save the checker in a variable, e.g.,
ANS(Real(10)->cmp->withPostFilter(...));or
ANS(num_cmp(10)->withPostFilter(...));A filter is a subroutine which takes one AnswerHash as an input, followed by a hash of options.
Usage: filter($ans_hash, option1 =>value1, option2=> value2 );
The filter performs some operations on the input AnswerHash and returns an AnswerHash as output.
Many AnswerEvaluator objects are merely a sequence of filters placed into three queues:
pre_filters: these normalize student input, prepare text and so forth
evaluators: these decide whether or not an answer is correct
post_filters: typically these clean up error messages or process errors
and generate error messages.If a filter detects an error it can throw an error message using the $rh_ans-throw_error()> method. This skips the AnswerHash by all remaining pre_filter $rh_ans-catch_error>, decides how ( or whether) it is supposed to handle the error and then passes the result on to the next post_filter.
Setting the flag $rh_ans-{done} = 1> will skip the AnswerHash past the remaining post_filters.