Database schema migrations are one obvious place where the idea of reversibility is useful (although there's not really a "do something in the middle" step). Ac

Database schema migrations are one obvious place where the idea of reversibility is useful (although there's not really a "do something in the middle" step). ActiveRecord migrations (used in Ruby on Rails) have a way to define a reversible process, and they include reversible calls for basic things like creating a table or adding a column. http://edgeguides.rubyonrails.org/active_record_migrations.html#using-reversible http://edgeguides.rubyonrails.org/active_record_migrations.h...