1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 |
------------------------------------------------------------------------------ --- Library with some operations for encapsulating search. --- Note that some of these operations are not fully declarative, --- i.e., the results depend on the order of evaluation and program rules. --- There are newer and better approaches the encapsulate search, --- in particular, set functions (see module `Control.SetFunctions` in --- package `setfunctions`), which should be used. --- --- @author Michael Hanus --- @version November 2022 ------------------------------------------------------------------------------ {-# LANGUAGE CPP #-} module Control.Findall ( getAllValues , allValues, someValue, oneValue , allSolutions, someSolution, oneSolution , isFail , rewriteAll, rewriteSome ) where --- Gets all values of an expression (currently, via an incomplete --- depth-first strategy). Conceptually, all values are computed --- on a copy of the expression, i.e., the evaluation of the expression --- does not share any results. In PAKCS, the evaluation suspends --- as long as the expression contains unbound variables or the computed --- values contain unbound variables. --- Similar to Prolog's findall. getAllValues :: a -> IO [a] getAllValues e = return (allValues e) --- Returns all values of an expression (currently, via an incomplete --- depth-first strategy). Conceptually, all values are computed on a copy --- of the expression, i.e., the evaluation of the expression does not share --- any results. In PAKCS, the evaluation suspends as long as the expression --- contains unbound variables or the computed --- values contain unbound variables. --- --- Note that this operation is not purely declarative since the ordering --- of the computed values depends on the ordering of the program rules. allValues :: a -> [a] allValues external --- Returns some value for an expression (currently, via an incomplete --- depth-first strategy). If the expression has no value, the --- computation fails. Conceptually, the value is computed on a copy --- of the expression, i.e., the evaluation of the expression does not share --- any results. In PAKCS, the evaluation suspends as long as the expression --- contains unbound variables or the computed --- value contains unbound variables. --- --- Note that this operation is not purely declarative since --- the computed value depends on the ordering of the program rules. --- Thus, this operation should be used only if the expression --- has a single value. someValue :: a -> a someValue external --- Returns just one value for an expression (currently, via an incomplete --- depth-first strategy). If the expression has no value, `Nothing` --- is returned. Conceptually, the value is computed on a copy --- of the expression, i.e., the evaluation of the expression does not share --- any results. In PAKCS, the evaluation suspends as long as the expression --- contains unbound variables or the computed --- value contains unbound variables. --- --- Note that this operation is not purely declarative since --- the computed value depends on the ordering of the program rules. --- Thus, this operation should be used only if the expression --- has a single value. oneValue :: a -> Maybe a oneValue external --- Returns all values satisfying a predicate, i.e., all arguments such that --- the predicate applied to the argument can be evaluated to `True` --- (currently, via an incomplete depth-first strategy). --- In PAKCS, the evaluation suspends as long as the predicate expression --- contains unbound variables or the computed --- values contain unbound variables. --- --- Note that this operation is not purely declarative since the ordering --- of the computed values depends on the ordering of the program rules. allSolutions :: Data a => (a -> Bool) -> [a] allSolutions p = allValues (invertPred p) --- Returns some value satisfying a predicate, i.e., some argument such that --- the predicate applied to the argument can be evaluated to `True` --- (currently, via an incomplete depth-first strategy). --- If there is no value satisfying the predicate, the computation fails. --- --- Note that this operation is not purely declarative since the ordering --- of the computed values depends on the ordering of the program rules. --- Thus, this operation should be used only if the --- predicate has a single solution. someSolution :: Data a => (a -> Bool) -> a someSolution p = someValue (invertPred p) --- Returns just one value satisfying a predicate. --- If there is no such value, `Nothing` is returned --- --- Note that this operation is not purely declarative since --- the computed value depends on the ordering of the program rules. --- Thus, this operation should be used only if the expression --- has a single value. oneSolution :: Data a => (a -> Bool) -> Maybe a oneSolution p = oneValue (invertPred p) -- Inverts a predicate, i.e., compute all values for which the predicate -- succeeds. invertPred :: Data a => (a -> Bool) -> a invertPred p | p x = x where x free --- Does the computation of the argument to a head-normal form fail? --- Conceptually, the argument is evaluated on a copy, i.e., --- even if the computation does not fail, it has not been evaluated. isFail :: a -> Bool isFail external ------------------------------------------------------------------------------ --- Gets all values computable by term rewriting. --- In contrast to `allValues`, this operation does not wait --- until all "outside" variables are bound to values, --- but it returns all values computable by term rewriting --- and ignores all computations that require bindings for outside variables. rewriteAll :: a -> [a] rewriteAll external --- Similarly to 'rewriteAll' but returns only some value computable --- by term rewriting. Returns `Nothing` if there is no such value. rewriteSome :: a -> Maybe a rewriteSome external |