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------------------------------------------------------------------------------ --- This library defines a data structure for sequence of values. --- It is used in search trees (module `SearchTree`) as well as in --- set functions (module `SetFunctions`). --- Using sequence of values (rather than standard lists of values) --- is necessary to get the behavior of set functions --- w.r.t. finite failures right, as described in the paper --- --- > J. Christiansen, M. Hanus, F. Reck, D. Seidel: --- > A Semantics for Weakly Encapsulated Search in Functional Logic Programs --- > Proc. 15th International Conference on Principles and Practice --- > of Declarative Programming (PPDP'13), pp. 49-60, ACM Press, 2013 --- --- Note that this is a simple implementation for PAKCS in order to provide --- some functionality used by other modules. --- In particular, the intended semantics of failures is not provided --- in this implementation. --- --- @author Fabian Reck, Michael Hanus --- @version February 2016 --- @category algorithm ------------------------------------------------------------------------------ module ValueSequence(ValueSequence, emptyVS, addVS, failVS, (|++|), vsToList) where --- A value sequence is an abstract sequence of values. --- It also contains failure elements in order to implement the semantics --- of set functions w.r.t. failures in the intended manner (only in KiCS2). data ValueSequence a = EmptyVS | ConsVS a (ValueSequence a) --- An empty sequence of values. emptyVS :: ValueSequence a emptyVS = EmptyVS --- Adds a value to a sequence of values. addVS :: a -> ValueSequence a -> ValueSequence a addVS = ConsVS --- Adds a failure to a sequence of values. --- The argument is the encapsulation level of the failure. failVS :: Int -> ValueSequence a failVS _ = EmptyVS -- cannot be implemented in PAKCS!" --- Concatenates two sequences of values. (|++|) :: ValueSequence a -> ValueSequence a -> ValueSequence a xs |++| ys = case xs of EmptyVS -> ys ConsVS z zs -> ConsVS z (zs |++| ys) --- Transforms a sequence of values into a list of values. vsToList :: ValueSequence a -> [a] vsToList EmptyVS = [] vsToList (ConsVS x xs) = x : vsToList xs |