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17 Solver types

Solver types are an experimental addition to the language supporting the implementation of constraint solvers. A program may place constraints on and between variables of a solver type, limiting the values those variables may take on before they are actually bound. For example, if X and Y are variables belonging to a constrained integer solver type, we might place constraints upon them such that X > 3 + Y and Y =< 7. A later attempt to unify Y with 10 will fail (it would violate the second constraint); similarly an attempt to unify X with 5 and Y with 4 would fail (it would violate the first constraint).