Hello,

Just a bit of minor academic nitpicking...
 
> Yeah.  After all, the "uniqueness constraint" has a theory with an
> excellent pedigree (IIUC linear logic, whose proof theory Clean uses
> here, goes back at least to the 60s, and Wadler proposed linear types
> for IO before anybody had heard of monads).  
>
Linear logic/typing does not quite capture uniqueness types since a term with a unique type can always be copied to become non-unique, but a linear type cannot become unrestricted.

As a historical note, the first paper on linear logic was published by Girard in 1987; but the purely linear core of linear logic has (non-commutative) antecedents in a system introduced by Lambek in a 1958 paper titled "The Mathematics of Sentence Structure".

-Jeff

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