1 files changed, 12 insertions, 1 deletions
diff --git a/discocaml/eval.ml b/discocaml/eval.ml
index 9c12003..f8f7dc2 100644
--- a/discocaml/eval.ml
+++ b/discocaml/eval.ml
@@ -38,6 +38,17 @@ let find_redex_cbv (ast : expr ast) : expr index option =
 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 =
+exception NotARedex of expr ast
+
+let reduce (ast : expr ast) (i : expr index) : expr ast =
+  let fail () = raise (NotARedex { ast with root = i }) in
   let ast = copy ast in
+  let must_int j = match get_subexpr ast j with Int n -> n | _ -> fail () in
+  Arraylist.set ast.subexprs i.index
+    (match get_subexpr ast i with
+    | App (_f, _x) -> failwith "TODO"
+    | Prim (Add, (l, r)) -> Int (must_int l + must_int r)
+    | Prim (Sub, (l, r)) -> Int (must_int l - must_int r)
+    | Prim (Mul, (l, r)) -> Int (must_int l * must_int r)
+    | _ -> fail ());
   ast