Merge pull request #246 from julianuu/master

sanitize more possible input schemata of frac

latexdiff

@@ -2570,15 +2570,15 @@ sub take_comments_and_newline_from_frac() {
   # some special magic for common usage of frac, which does not conform to the latexdiff requirements but can be made to fit
   # note that this is a rare exception to the general rule that the new tex can be reconstructed from the diff file
 
-  # \frac12 -> \frac{1}{2}
-  s/\\frac(\d)(\w)/\\frac\{$1\}\{$2\}/g;
-
-  # \frac1{2b} -> \frac{1}{2b}
-  s/\\frac(\d)/\\frac\{$1\}/g;
-
-  # delete space and comment characters between \frac arguments
-#  s/\\frac(?:\s*?%[^\n]*?)*?(\{$pat_n\})\s*(\{$pat_n\})/\\frac$1$2/g;
-  s/\\frac(?:\s|%[^\n]*?)*(\{$pat_n\})(?:\s|%[^\n]*?)*(\{$pat_n\})/\\frac$1$2/g;
+  # regex that matches space and comment characters
+  my $space = qr/\s|%[^\n]*?/;
+  # \frac {abc} -> \frac{abc}
+  # \frac1 -> \frac{1}
+  # \frac a -> \frac{a}
+  # \frac \lambda -> \frac{\lambda}
+  s/\\frac(?|${space}+\{($pat_n)\}|${space}*(\d)|${space}+(\w)|${space}*(\\[a-zA-Z]+))/\\frac\{$1\}/g;
+  # same as above for the second argument of frac
+  s/\\frac(\{$pat_n\})(?|${space}*\{($pat_n)\}|${space}*(\d)|${space}+(\w)|${space}*(\\[a-zA-Z]+))/\\frac$1\{$2\}/g;
 }
 
 # preprocess($string, ..)