Preface_core.MonoidSourceA generic monoid.
times_nel combine n x apply combine on x n times. If n is lower than 1 the function will returns None .
times combine neutral n x apply combine on x n times. If n is lower than 1 the function will returns neutral .
reduce_nel combine list Reduce a Nonempty_list.t using combine.
reduce combine neutral list Reduce a list using combine and neutral as initial value.