Change the "teacher's answer" output of strings to remove quotes and maths environments.

Needed for Parson block output, but a general improvement.

stack/input/string/string.class.php

@@ -100,8 +100,8 @@ class stack_string_input extends stack_algebraic_input {
             return '';
         }
 
-        $value = stack_utils::maxima_string_to_php_string($value);
-        return stack_string('teacheranswershow', array('value' => '<code>'.$value.'</code>', 'display' => $display));
+        $display = stack_utils::maxima_string_strip_mbox($display);
+        return stack_string('teacheranswershow_disp', array('display' => $display));
     }
 
     /**

stack/utils.class.php

@@ -781,6 +781,7 @@ class stack_utils {
         $converted = str_replace("\"", "\\\"", $converted);
         return '"' . $converted . '"';
     }
+
     /**
      * Converts a PHP string object containing a Maxima string as presented by the grind command to a PHP string object.
      * @param a string that contains ""-quotes around the content.
@@ -792,6 +793,22 @@ class stack_utils {
         return substr($converted, 1, -1);
     }
 
+    /**
+     * Remove redundant "mbox" environments from Latex equations strings containing just strings.
+     * @param a string that contains ""-quotes around the content.
+     * @return a string without those quotes.
+     */
+    public static function maxima_string_strip_mbox($string) {
+        $converted = trim($string);
+        if (substr($converted, 0, 2) == '\(' || substr($converted, 0, 2) == '\[') {
+            $converted = substr($converted, 2, -2);
+        }
+        if (substr(trim($converted), 0, 6) == '\mbox{') {
+            return substr(trim($converted), 6, -1);
+        }
+        return $string;
+    }
+
     /**
      * Translate some strings from Maxima.
      * @param string $string

tests/input_string_test.php

@@ -57,9 +57,7 @@ class input_string_test extends qtype_stack_testcase {
                 .'style="width: 13.6em" autocapitalize="none" spellcheck="false" class="maxima-string" value="0" />',
                 $el->render(new stack_input_state(stack_input::VALID, array('0'), '', '', '', '', ''),
                         'stack1__ans1', false, null));
-        $this->assertEquals('The answer <span class="filter_mathjaxloader_equation"><span class="nolink">' .
-                '\( \\mbox{Hello world} \)</span></span>, which can be typed as <code>Hello world</code>, ' .
-                'would be correct.',
+        $this->assertEquals('The answer Hello world would be correct.',
                 $el->get_teacher_answer_display('"Hello world"', '\\mbox{Hello world}'));
     }
 
@@ -72,9 +70,7 @@ class input_string_test extends qtype_stack_testcase {
         $this->assertEquals(stack_input::VALID, $state->status);
         $this->assertEquals('"Hello world"', $state->contentsmodified);
         $this->assertEquals('\[ \mbox{Hello world} \]', $state->contentsdisplayed);
-        $this->assertEquals('The answer <span class="filter_mathjaxloader_equation">' .
-                '<span class="nolink">\[ \[ \mbox{Hello world} \]</span></span> \), ' .
-                'which can be typed as <code>Hello world</code>, would be correct.',
+        $this->assertEquals('The answer Hello world would be correct.',
                 $el->get_teacher_answer_display($state->contentsmodified, $state->contentsdisplayed));
     }