Description 1ML is a reboot of ML starting from first-class modules, and unifies core and module layer into one small and consistent language. It is described in the following papers: Andreas Rossberg. 1ML — core and modules united. ICFP 2015. Andreas Rossberg. 1ML — core and modules united (Extended). 2015. Expanded version including Technical Appendix. Andreas Rossberg. 1ML — core and modules un