Gatsby uses filenames to generate urls and look up special pages like custom error pages. BuckleScript unfortunately does not support as wide a range of filenames due to filenames being used to generate module names. For the porting of this project specifically the consequences are:
404.re is not valid, the code for the custom error page has been put in error404.re and a 404.js that simply re-exports error404 has been aded as a bridge.page-2.re has been renamed to page_2.re, which of course causes the generated url to use an underscore instead of a dash too.index.re is causing significant problems. The solution currently used is to rename the file to something unique, e.g. layouts_index.re, then add an index.js that re-exports it.