[clean-list] instantiation of attributed type variables

[Wolfgang Jeltsch]

Hello again,

how are type variables instantiated in the uniqueness typing system described 
in "Uniqueness Typing for Functional Programming with Graph Rewriting 
Semantics"?  Is a type variable replaced by a type without a top-level 
attribute (since the variable provides the attribute) or is the variable 
together with the attribute replaced by a uniqueness type which has the same 
attribute.

Take, for example, the type a^* -> a^x where ^* means "unique" and ^x means 
"non-unique".  If the first of the above variants is true, this type can be 
specialized to Integer^* -> Integer^x by replacing a with Integer.  If the 
second variant is true, no specialization is possible, since each occurence 
of the type variable a together with an uniqueness attribute has to be 
replaced with the same attributed type but this type has to have ^* as well 
as ^x as its uniqueness attribute because the type variable a appears with 
both attributes in the above function type.

Best regards,
Wolfgang