On windows, the 'unixFilter' function used window's 'createProcess' function to create the external process that will filter some String input. The problem with this is that it is unable to execute batch stubs (eg. anything created using 'gem install ...') even if its in $PATH. Anyways a solution to this issue is to execute the batch file explicitly using 'cmd /c batchfile' but there is no rational way to know where said batchfile is on the system. My solution is to detect windows using the System.Info module and then instead of using 'proc' to create the function, use 'shell' instead which will be able to execute everything 'proc' can + batch files. Inspired by: http://www.blaenkdenum.com/posts/the-switch-to-hakyll/#scss Signed-off-by: Collin J. Doering <rekahsoft@gmail.com>