Home » forums » LtU Forum Really un-mutable Scheme Didn't notice this being mentioned on LtU yet: PLT is going really really un-mutable, which seems like a rather cool and worthy experiment to my mind, and will probably highlight some of the more pragmatic and cultural aspects of managing the development of a language in light of the user community. For PLT Scheme v4.0, weâ€™re going to try it. In our main dialects of Scheme (such as the mzscheme language), cons will create immutable pairs, and pair? and list? will recognize only immutable pairs and lists. The set-car! and set-cdr procedures will not exist. A new set of procedure mcons, mcar, mcdr, set-mcar!, and set-mcdr! will support mutable pairs. Comment viewing options Flat list - collapsed Flat list - expanded Threaded list - collapsed Threaded list - expanded Date - newest first Date - oldest first Select your preferred way to display the comments and click "Save settings" to activate your changes.