[WWcvs] pg: Added ability to have answers that are empty strings.

[dpvc v. a. <we...@ma...>]

Log Message:
-----------
Added ability to have answers that are empty strings.  String("") now
will produce a valid string object regardless of the Context's defined
string values.  (You can prevent this using

       Context()->flags->set(allowEmptyStrings=>0);

if you wish).  String("")->cmp will produce an answer checker for an
empty string (it removes the blank checker that WW installs).

Modified Files:
--------------
    pg/lib:
        Parser.pm
        Value.pm
    pg/lib/Parser:
        String.pm
    pg/lib/Value:
        AnswerChecker.pm
        String.pm

Revision Data
-------------
Index: Value.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value.pm,v
retrieving revision 1.47
retrieving revision 1.48
diff -Llib/Value.pm -Llib/Value.pm -u -r1.47 -r1.48
--- lib/Value.pm
+++ lib/Value.pm
@@ -24,8 +24,9 @@
     #
     ijk => 0,  # print vectors as <...>
     #
-    #  word to use for infinity
+    #  For strings:
     #
+    allowEmptyStrings => 1,
     infiniteWord => 'infinity',
     #
     #  For intervals and unions:
@@ -174,7 +175,7 @@
 #
 sub makeValue {
   my $x = shift; my %params = (showError => 0, makeFormula => 1, @_);
-  return $x if (ref($x) && ref($x) ne 'ARRAY') || $x eq '';
+  return $x if ref($x) && ref($x) ne 'ARRAY';
   return Value::Real->make($x) if matchNumber($x);
   if (matchInfinite($x)) {
     my $I = Value::Infinity->new();
@@ -182,7 +183,8 @@
     return $I;
   }
   return Value::String->make($x)
-    if (!$Parser::installed || $$Value::context->{strings}{$x});
+    if !$Parser::installed || $$Value::context->{strings}{$x} ||
+       ($x eq '' && $$Value::context->{flags}{allowEmptyStrings});
   return $x if !$params{makeFormula};
   Value::Error("String constant '%s' is not defined in this context",$x)
     if $params{showError};
@@ -256,6 +258,7 @@
   elsif (ref($value)) {return 'unknown'}
   elsif (defined($strings->{$value})) {return 'String'}
   elsif (Value::isNumber($value)) {return 'Number'}
+  elsif ($value eq '' && $equation->{context}{flags}{allowEmptyStrings}) {return 'String'}
   return 'unknown';
 }
 
Index: Parser.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Parser.pm,v
retrieving revision 1.30
retrieving revision 1.31
diff -Llib/Parser.pm -Llib/Parser.pm -u -r1.30 -r1.31
--- lib/Parser.pm
+++ lib/Parser.pm
@@ -39,7 +39,10 @@
     my $tree = $string; $tree = $tree->{tree} if exists $tree->{tree};
     $math->{tree} = $tree->copy($math);
   } elsif (Value::isValue($string)) {
-    $math->{tree} = $math->{context}{parser}{Value}->new($math,$string);
+    $math->{tree} = $context->{parser}{Value}->new($math,$string);
+  } elsif ($string eq '' && $context->{flags}{allowEmptyStrings}) {
+    $math->{string} = "";
+    $math->{tree} = $context->{parser}{Value}->new($math,"");
   } else {
     $math->{string} = $string;
     $math->tokenize;
Index: String.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Parser/String.pm,v
retrieving revision 1.10
retrieving revision 1.11
diff -Llib/Parser/String.pm -Llib/Parser/String.pm -u -r1.10 -r1.11
--- lib/Parser/String.pm
+++ lib/Parser/String.pm
@@ -19,7 +19,7 @@
   my $def = $equation->{context}{strings}{$value};
   unless ($def) {
     $def = $equation->{context}{strings}{uc($value)};
-    $def = undef if $def->{caseSensitive} && $value ne uc($value);
+    $def = {} if $def->{caseSensitive} && $value ne uc($value);
   }
   $value = $def->{alias}, $def = $equation->{context}{strings}{$value}
     while defined($def->{alias});
Index: AnswerChecker.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/AnswerChecker.pm,v
retrieving revision 1.65
retrieving revision 1.66
diff -Llib/Value/AnswerChecker.pm -Llib/Value/AnswerChecker.pm -u -r1.65 -r1.66
--- lib/Value/AnswerChecker.pm
+++ lib/Value/AnswerChecker.pm
@@ -617,6 +617,25 @@
   return $typeMatch->typeMatch($other,$ans);
 }
 
+#
+#  Remove the blank-check prefilter when the string is empty,
+#  and add a filter that removes leading and trailing whitespace.
+#
+sub cmp {
+  my $self = shift;
+  my $cmp = $self->SUPER::cmp(@_);
+  if ($self->value =~ m/^\s*$/) {
+    $cmp->install_pre_filter('erase');
+    $cmp->install_pre_filter(sub {
+      my $ans = shift;
+      $ans->{student_ans} =~ s/^\s+//g;
+      $ans->{student_ans} =~ s/\s+$//g;
+      return $ans;
+    });
+  }
+  return $cmp;
+}
+
 #############################################################
 
 package Value::Point;
Index: String.pm
===================================================================
RCS file: /webwork/cvs/system/pg/lib/Value/String.pm,v
retrieving revision 1.7
retrieving revision 1.8
diff -Llib/Value/String.pm -Llib/Value/String.pm -u -r1.7 -r1.8
--- lib/Value/String.pm
+++ lib/Value/String.pm
@@ -21,7 +21,8 @@
   my $self = shift; my $class = ref($self) || $self;
   my $x = join('',@_);
   my $s = bless {data => [$x]}, $class;
-  if ($Parser::installed) {
+  if ($Parser::installed &&
+      !($x eq '' && $$Value::context->flag('allowEmptyStrings'))) {
     my $strings = $$Value::context->{strings};
     if (!$strings->{$x}) {
       my $X = $strings->{uc($x)};