| topic started 5/22/2000; 9:48:23 PM last post 5/22/2000; 9:48:23 PM |
5/22/2000; 9:48:23 PM (reads: 2977, responses: 0) |
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NAMEWeBWorK::PG::Translator - Evaluate PG code and evaluate answers safely
SYNPOSISmy $pt = new WeBWorK::PG::Translator; # create a translator; $pt -> unrestricted_load("${courseScriptsDirectory}PG.pl");
$pt ->translate(); # translate the problem (the out following 4 pieces of $pt -> process_answers(\%inputs); # evaluates all of the answers using submitted
DESCRIPTIONThis module defines an object which will translate a problem written in the Problem Generating (PG) language
be_strictThis creates a substitute for BEGIN {
evaluate_modules Usage: $obj -> evaluate_modules('WWPlot', 'Fun', 'Circle');
Adds the modules WWPlot.pm, Fun.pm and Circle.pm in the courseScripts directory to the list of modules which can be used by the PG problems. The keyword 'reset' or 'erase' erases the list of modules already loaded
new Creates the translator object.(b) The following routines defined within the PG module are shared: &be_strict &includePGtext &PG_answer_eval &send_mail_to In addition the environment hash <A href = (c) Sharing macros: The macros shared with the safe compartment are '&read_whole_problem_file'
Safe compartment pass through macros
set_mask(e) Now we close the safe compartment. Only the certain operations can be used within PG problems and the PG macro files. These include the subroutines shared with the safe compartment as defined above and most Perl commands which do not involve file access, access to the system or evaluation. Specifically the following are allowed time() The following are specifically not allowed: eval()
PG_errorMessageThis routine processes error messages by fixing file names and adding
traceback information. It loops through the function calls via
We skip any nested calls to Parser:: or Value:: so that these act more like perl built-in functions. We stop when we find a routine in the WeBWorK:: package, or an __ANON__ routine, in order to avoid reporting the PG translator calls that surround the pg file. Finally, there is usually one more eval before that, so we remove it as well. File names are shortened, when possible, by replacing the templates directory with [TMPL], the WeBWorK root directory by [WW] and the PG root directory by [PG]. =cut sub PG_errorMessage {
my $return = shift; my $frame = 2;
my $message = join("\n",@_); $message =~ s/\.?\s+$//;
my $files = eval ('$main::__files__'); $files = {} unless $files;
my $tmpl = $files->{tmpl} || '$';
my $root = $files->{root} || '$';
my $pg = $files->{pg} || '$';
#
# Fix initial message file names
#
$message =~ s! $tmpl! [TMPL]!g; $message =~ s! $root! [WW]!g; $message =~ s!
$pg! [PG]!g;
$message =~ s/(\(eval \d+\)) (line (\d+))/$2 of $1/;
while ($message =~ m/of (?:file )?(\(eval \d+\))/ && defined($files->{$1})) {
my $name = $files->{$1};
$name =~ s!^$tmpl![TMPL]!; $name =~ s!^$root![WW]!; $name =~ s!^$pg![PG]!;
$message =~ s/\(eval \d+\)/$name/g;
}
#
# Return just the message if that's all we want, or
# if the message already includes a stack trace
#
return $message."\n" if $return eq 'message' || $message =~ m/\n Died within/;
#
# Look through caller stack for traceback information
#
my @trace = ($message);
my $skipParser = (caller(3))[3] =~ m/^(Parser|Value)::/;
while (my ($pkg,$file,$line,$subname) = ############################################################################
Translate(3) Preprocess the problem text The input text is subjected to two global replacements. First every incidence of BEGIN_TEXT is replaced by TEXT( EV3( <<'END_TEXT' ) ); The first construction is syntactic sugar for the second. This is explained
in Second every incidence of \ (backslash) is replaced by \\ (double backslash). Third each incidence of ~~ is replaced by a single backslash. This is done to alleviate a basic incompatibility between TeX and Perl. TeX uses backslashes constantly to denote a command word (as opposed to text which is to be entered literally). Perl uses backslash to escape the following symbol. This escape mechanism takes place immediately when a Perl script is compiled and takes place throughout the code and within every quoted string (both double and single quoted strings) with the single exception of single quoted "here" documents. That is backlashes which appear in TEXT(<<'EOF'); are the only ones not immediately evaluated. This behavior makes it very difficult to use TeX notation for defining mathematics within text. The initial global replacement, before compiling a PG problem, allows one to use backslashes within text without doubling them. (The anomolous behavior inside single quoted "here" documents is compensated for by the behavior of the evaluation macro EV3.) This makes typing TeX easy, but introduces one difficulty in entering normal Perl code. The second global replacement provides a work around for this -- use ~~ when you would ordinarily use a backslash in Perl code. In order to define a carriage return use ~~n rather than \n; in order to define a reference to a variable you must use ~~@array rather than \@array. This is annoying and a source of simple compiler errors, but must be lived with. The problems are not evaluated in strict mode, so global variables can be used without warnings. (4) Evaluate the problem text Evaluate the text within the safe compartment. Save the errors. The safe compartment is a new one unless the $safeCompartment was set to zero in which case the previously defined safe compartment is used. (See item 1.) (5) Process errors The error provided by Perl is truncated slightly and returned. In the text string which would normally contain the rendered problem. The original text string is given line numbers and concatenated to the errors. (6) Prepare return values Returns:
Answer evaluation methods
access methods$obj->rh_student_answers
process_answers$obj->process_answers()
grade_problem$obj->rh_problem_state(%problem_state); # sets the current problem state
PGsortBecause of the way sort is optimized in Perl, the symbols $a and $b have special significance.
sorts the list numerically and lexically respectively. If PGsort sub { $_[0] < $_[1] }, @list;
(called num_sort and lex_sort) provide slightly slower, but safer, routines for the PG language. (The subroutines for ordering are required. Note the commas!)
includePGtextincludePGtext($string_ref, $envir_ref) Calls
PG_restricted_evalPG_restricted_eval($string) Evaluated in package 'main'. Result of last statement is returned. When called from within a safe compartment the safe compartment package is 'main'. File path = /ww/webwork/pg/lib/WeBWorK/PG/Translator.pm |