Thanks for your input, Unfortunately I don't have a clear design yet, I know one drawback which would be that one might need SMT solvers which would require hell lot of convincing for why should rustc be shipped with that 
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It will take some time before I can have a preliminary design, that would be especially hard because the easy solution as described by @ canndrew would require intrusive modifications to the standard library, and i am trying to figure away to get away with extending the language rather than having to rewrite stdlib before making the extension useful.