encode relations on module base

1 files changed, 36 insertions, 0 deletions

diff --git a/lib/prelude/standard.ml b/lib/prelude/standard.ml
new file mode 100644
index 0000000..43ffc44
--- /dev/null
+++ b/lib/prelude/standard.ml
@@ -0,0 +1,36 @@
+let less_than_natural: Relation.t =
+  let rec generator (position: int option): Generator.result =
+    let pair_of_nat n =
+      let nf = float_of_int n in
+      let r =
+        int_of_float (floor ((1. +. sqrt (1. +. 8. *. nf)) /. 2.))
+      in
+      let t_prev = (r * (r - 1)) / 2 in
+      let left = n - t_prev in
+      (left, r) in
+    match position with
+    | Some position -> 
+      let (left: Conventions.AbstractValue.t), (right: Conventions.AbstractValue.t) =
+        let (left_value, right_value) = pair_of_nat position in
+        ({ fields = Conventions.AbstractValue.StringMap.of_list [("value", string_of_int left_value)] }, 
+         { fields = Conventions.AbstractValue.StringMap.of_list [("value", string_of_int right_value)] })
+      in let attributes: Conventions.AbstractValue.t Tuple.AttributeMap.t =
+        Tuple.AttributeMap.of_list [("left", left); ("right", right)]
+      in Generator.Value (Tuple.make_materialized ~relation: "less_than" ~attributes: attributes, generator)
+    | None -> Error "Cannot produce a randomly enumerated value for less_than over naturals."
+  in let membership_criteria: Tuple.t -> bool = function 
+        | Tuple.Materialized materialized -> 
+            let left = Tuple.AttributeMap.find "left" materialized.attributes
+            in let right = Tuple.AttributeMap.find "right" materialized.attributes
+            in left < right
+        | Tuple.NonMaterialized _non_materialized -> false (* TODO: Handle references later *)
+  in Relation.make 
+    ~hash: None
+    ~name: "natural_natural_less_than"
+    ~tree: None
+    ~constraints: None
+    ~cardinality: Conventions.Cardinality.AlephZero
+    ~generator: (Some generator)
+    ~membership_criteria: membership_criteria
+    ~provenance: (Relation.Provenance.Base "less_than")
+    ~lineage: (Relation.Lineage.Base "less_than")
\ No newline at end of file