I think it is nice in Haskell to retain the ability to control the underlying representation of a string. The laziness allows the native linked list representation without the user having to know about the underlying representation. Your memory mapping function can simply return a lazy linked list of chars in Haskell as well. If the underlying representation turns out to be inefficient on the current system, then that can always be tuned by the user. Maybe in Prolog it is sufficient to leave all of that to the runtime system.

Thanks for the Prolog tips. I had a look at clpqr, and could not find any reference to boolean variables and operators. Maybe clpqr intersects with another system whose docs do refer to boolean variables. I could not see how to combine clpqr with clpb. Basically what I would like is for certain linear constraints to be active only if other chosen boolean expressions are true.

Example: Choose energy price based on maximum power usage over past month. There are some Japanese electricity tariffs which do this. There would be a partition of maximum power usage ranges, and each range is associated with a price. Associate a binary variable to each range. Ensure exactly one of the variables is true (sum = 1). Create a range constraint over the maximum power usage for each partition, and multiply the bounds of that constraint with the associated binary variable. When a binary variable is set to zero, you have a trivial constraint.

It is indeed possible to represent boolean constraints as linear constraints over binary variables and develop a DSL to translate in this direction. I am wondering whether a system exists which allows easy expression of linear and boolean combined, and which provides tools for solving them efficiently.