2 files changed, 96 insertions, 0 deletions
diff --git a/lib/concepts/Relation.ml b/lib/concepts/Relation.ml
new file mode 100644
index 0000000..a4fb341
--- /dev/null
+++ b/lib/concepts/Relation.ml
@@ -0,0 +1,81 @@
+type address = Hash.hash
+type schema = string BatMap.String.t
+
+type t =
+  { name: string;
+    tuples: address;
+    schema: schema }
+
+module Field = struct
+  let name = "name"
+  let tuples = "tuples"
+  let schema = "schema"
+end
+
+module Error = struct
+  open Condition
+
+  let malformed_relation () =
+    condition "relation-malformed" "A relation representation did not conform to what was expected"
+      empty
+
+  let malformed_hash length =
+    condition "relation-malformed-hash" "A relation tuple root was not a valid hash"
+      ("length" |=| Value.Integer length)
+end
+
+let make ~name ~tuples ~schema = {name; tuples; schema}
+
+let name relation = relation.name
+let tuples relation = relation.tuples
+let schema relation = relation.schema
+
+let schema_empty = BatMap.String.empty
+
+let schema_of_list fields =
+  List.fold_left (fun acc (name, domain) -> BatMap.String.add name domain acc) schema_empty
+    fields
+
+let schema_to_list schema = BatMap.String.bindings schema
+
+let schema_to_bencode schema =
+  Codec.Bencode.Dict
+    (schema_to_list schema
+    |> List.map (fun (name, domain) -> name, Codec.Bencode.String domain) )
+
+let schema_of_bencode value =
+  let open Utilities.Result in
+  let* fields = Codec.Bencode.as_dict value in
+  fields
+  |> List.map (fun (name, domain) ->
+         let* domain = Codec.Bencode.as_string domain in
+         Ok (name, domain) )
+  |> sequence
+  |> Result.map schema_of_list
+
+module Body = struct
+  type nonrec t = t
+
+  let tag = 'r'
+  let malformed = Error.malformed_relation
+
+  let equal left right =
+    left.name = right.name
+    && Hash.hash_equals left.tuples right.tuples
+    && BatMap.String.equal String.equal left.schema right.schema
+
+  let fields relation =
+    [ Field.name, Object.Field.string relation.name;
+      Field.schema, schema_to_bencode relation.schema;
+      Field.tuples, Object.Field.address relation.tuples ]
+
+  let of_fields data =
+    let open Utilities.Result in
+    let* name = Object.Field.require_string Field.name data in
+    let* tuples = Object.Field.require_address ~malformed:Error.malformed_hash Field.tuples data in
+    let* schema_data = Codec.Bencode.field Field.schema data in
+    let* schema = schema_of_bencode schema_data in
+    Ok {name; tuples; schema}
+end
+
+include (Object.Codec.Make (Body) : Object.S with type t := t)
diff --git a/lib/concepts/Relation.mli b/lib/concepts/Relation.mli
new file mode 100644
index 0000000..5319a3d
--- /dev/null
+++ b/lib/concepts/Relation.mli
@@ -0,0 +1,15 @@
+type t
+type address = Hash.hash
+type schema
+
+include Object.S with type t := t
+
+val make : name:string -> tuples:address -> schema:schema -> t
+
+val name : t -> string
+val tuples : t -> address
+val schema : t -> schema
+
+val schema_empty : schema
+val schema_of_list : (string * string) list -> schema
+val schema_to_list : schema -> (string * string) list