Use GADTs for prims, actual redex finding.

1 files changed, 41 insertions, 3 deletions

diff --git a/discocaml/eval.ml b/discocaml/eval.ml
index 816d269..9c12003 100644
--- a/discocaml/eval.ml
+++ b/discocaml/eval.ml
@@ -1,5 +1,43 @@
 open Ast
 
-let find_redex_cbv : expr ast -> expr index option = function _ -> None
-let find_redex_cbn : expr ast -> expr index option = function _ -> None
-let reduce : expr ast -> expr index -> expr ast = fun e _ -> e
+let or_else (type a) (l : a option) (r : a option Lazy.t) : a option =
+  match l with Some x -> Some x | None -> Lazy.force r
+
+let is_redex (ast : expr ast) (i : expr index) : bool =
+  match get_subexpr ast i with
+  | App (f, _) -> (
+      match get_subexpr ast f with Lam (_, _) -> true | _ -> false)
+  | Int _ -> false
+  | Lam (_, _) -> false
+  | Prim (Add, (l, r)) | Prim (Sub, (l, r)) | Prim (Mul, (l, r)) -> (
+      match (get_subexpr ast l, get_subexpr ast r) with
+      | Int _, Int _ -> true
+      | _ -> false)
+  | Var _ -> false
+
+let find_redex_cbv_in (_ast : expr ast) (_i : expr index) : expr index option =
+  None
+
+let find_redex_cbn_in (ast : expr ast) : expr index -> expr index option =
+  let rec loop (i : expr index) : expr index option =
+    if is_redex ast i then Some i
+    else
+      match get_subexpr ast i with
+      | App (f, x) -> or_else (loop f) (lazy (loop x))
+      | Int _ -> None
+      | Lam (_, _) -> None
+      | Prim (Add, (l, r)) | Prim (Sub, (l, r)) | Prim (Mul, (l, r)) ->
+          or_else (loop l) (lazy (loop r))
+      | Var _ -> None
+  in
+  loop
+
+let find_redex_cbv (ast : expr ast) : expr index option =
+  find_redex_cbv_in ast ast.root
+
+let find_redex_cbn (ast : expr ast) : expr index option =
+  find_redex_cbn_in ast ast.root
+
+let reduce (ast : expr ast) (_i : expr index) : expr ast =
+  let ast = copy ast in
+  ast