diff --git a/lib/basic_block.ml b/lib/basic_block.ml
new file mode 100644
index 0000000..3617d8c
--- /dev/null
+++ b/lib/basic_block.ml
@@ -0,0 +1,20 @@
+type id = int
+type ir_array = Ir.t BatDynArray.t
+
+type t = {
+  id : id;
+  contents : ir_array;
+}
+
+let id_gen =
+  let id = ref 0 in
+  fun () ->
+    let result = !id in
+    id := !id + 1;
+    result
+
+let make () = { id = id_gen (); contents = BatDynArray.create () }
+let id_of basic_block = basic_block.id
+let label_of basic_block = ".L" ^ string_of_int basic_block.id
+let add basic_block ir = BatDynArray.add basic_block.contents ir
+let to_list basic_block = BatDynArray.to_list basic_block.contents
diff --git a/lib/basic_block.mli b/lib/basic_block.mli
new file mode 100644
index 0000000..28329ac
--- /dev/null
+++ b/lib/basic_block.mli
@@ -0,0 +1,22 @@
+(** [id] is unique identifier of the basic block. *)
+type id
+
+(** [t] is a basic block.. *)
+type t
+
+(** [make ()] is a new basic block. *)
+val make : unit -> t
+
+(** [id_of basic_block] is the identifier of [basic_block]. *)
+val id_of : t -> id
+
+(** [label_of basic_block] is the label of [basic_block] suitable for emission
+    in an object file as a symbol. *)
+val label_of : t -> string
+
+(** [add basic_block ir] adds [ir] to the end of [basic_block]. *)
+val add : t -> Ir.t -> unit
+
+(** [to_list basic_block] are the IR operations in [basic_block] in order as a
+    list. *)
+val to_list : t -> Ir.t list
diff --git a/lib/ir.ml b/lib/ir.ml
new file mode 100644
index 0000000..c3e0aac
--- /dev/null
+++ b/lib/ir.ml
@@ -0,0 +1,28 @@
+module Variable : sig
+  (** The type of an IR variable. *)
+  type t
+
+  (** [to_string var] is [var] as a string. *)
+  val to_string : t -> string
+end = struct
+  open Util
+
+  type t = int
+
+  let to_string = string_of_int >> ( ^ ) "i"
+end
+
+type constant = int
+
+(* todo *)
+type t =
+  | Add of Variable.t * Variable.t
+  | IAdd of Variable.t * constant
+  | Store of Variable.t * Variable.t
+  | IStore of Variable.t * constant
+  | Load of Variable.t * Variable.t
+  | ILoad of Variable.t * constant
+  | Param of Variable.t
+  | IParam of constant
+  | Jump of Basic_block.id
+  | Call of Basic_block.id
diff --git a/lib/x86.ml b/lib/x86.ml
new file mode 100644
index 0000000..e69de29
diff --git a/lib/x86.mli b/lib/x86.mli
new file mode 100644
index 0000000..e69de29