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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
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) : 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))
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
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
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
|
