exceptions as control flow lmao

1 files changed, 44 insertions, 33 deletions

diff --git a/discocaml/eval.ml b/discocaml/eval.ml
index a5cfe41..aa90d41 100644
--- a/discocaml/eval.ml
+++ b/discocaml/eval.ml
@@ -1,53 +1,64 @@
 open Ast
 
-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
+exception FoundRedex of expr index
 
-let is_redex (ast : expr ast) (i : expr index) : bool =
+let check_redex (ast : expr ast) (i : expr index) : unit =
   match get_subexpr ast i with
   | App (f, _) -> (
-      match get_subexpr ast f with Lam (_, _) -> true | _ -> false)
-  | Int _ -> false
-  | Lam (_, _) -> false
+      match get_subexpr ast f with
+      | Lam (_, _) -> raise (FoundRedex i)
+      | _ -> ())
+  | Int _ -> ()
+  | Lam (_, _) -> ()
   | 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
+      | Int _, Int _ -> raise (FoundRedex i)
+      | _ -> ())
+  | Var _ -> ()
 
-let find_redex_cbv_in (ast : expr ast) : expr index -> expr index option =
-  let rec loop (i : expr index) : expr index option =
-    or_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)
-      (lazy (if is_redex ast i then Some i else None))
+let find_redex_cbv_in (ast : expr ast) : expr index -> unit =
+  let rec loop (i : expr index) : unit =
+    (match get_subexpr ast i with
+    | App (f, x) ->
+        loop f;
+        loop x
+    | Int _ -> ()
+    | Lam (_, _) -> ()
+    | Prim (Add, (l, r)) | Prim (Sub, (l, r)) | Prim (Mul, (l, r)) ->
+        loop l;
+        loop r
+    | Var _ -> ());
+    check_redex ast i
   in
   loop
 
-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
+let find_redex_cbn_in (ast : expr ast) : expr index -> unit =
+  let rec loop (i : expr index) : unit =
+    check_redex ast i;
+    match get_subexpr ast i with
+    | App (f, x) ->
+        loop f;
+        loop x
+    | Int _ -> ()
+    | Lam (_, _) -> ()
+    | Prim (Add, (l, r)) | Prim (Sub, (l, r)) | Prim (Mul, (l, r)) ->
+        loop l;
+        loop r
+    | Var _ -> ()
   in
   loop
 
 let find_redex_cbv (ast : expr ast) : expr index option =
-  find_redex_cbv_in ast ast.root
+  try
+    find_redex_cbv_in ast ast.root;
+    None
+  with FoundRedex i -> Some i
 
 let find_redex_cbn (ast : expr ast) : expr index option =
-  find_redex_cbn_in ast ast.root
+  try
+    find_redex_cbn_in ast ast.root;
+    None
+  with FoundRedex i -> Some i
 
 exception NotARedex of expr ast