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(* algebra.ml — plan compilation support.
Generator-based evaluation is removed; all query execution goes through the
Tarski VM via Nt.execute_query. This module retains only what is needed to
construct plan nodes and handle compile-time errors. *)
type error = UnsupportedOperator of string
(* const_relation is kept for the Ast.Const case which produces an in-memory
ephemeral relation from literal pairs. It is used only in DRL tests and
REPL exploration; it does not go through the VM.
TODO: materialise const tuples into InMemoryBackend and SCAN them so they
can participate in VM JOINs. *)
let const_relation (pairs : (string * Conventions.AbstractValue.t) list) : Relation.ephemeral =
let make_gen () =
let attrs =
List.fold_left
(fun acc (k, v) -> Tuple.AttributeMap.add k {Attribute.value= v} acc)
Tuple.AttributeMap.empty pairs
in
let tuple = Tuple.Materialized {Tuple.relation= "const"; attributes= attrs} in
let gen = function
| None | Some 0 -> Generator.Value (tuple, fun _ -> Generator.Done)
| _ -> Generator.Done
in
gen
in
let schema = List.map (fun (k, _) -> k, "abstract") pairs in
new Relation.ephemeral
~name:"const" ~schema ~constraints:None ~cardinality:(Conventions.Cardinality.Finite 1)
~membership_criteria:(fun _ -> true)
~lineage:None ~provenance:None ~generator:(make_gen ())
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