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[@@@ocaml.text "/*"]
(** Copyright 2026, Dmitry Arzhaev *)
(** SPDX-License-Identifier: LGPL-3.0-or-later *)
[@@@ocaml.text "/*"]
open Ast
open Utils
type state = int [@@deriving show]
type ereclabel =
| ENonrec
| ERec of string
[@@deriving show]
type value =
| VInt of int
| VFloat of float
| VBool of bool
| VClosure of closure
| VUnit
and closure =
{ param : string
; body : expr
; env : value Table.t
; label : ereclabel
}
[@@deriving show]
type toplevel_value =
| VLet of string * value
| VExpr of value
type runtime_error =
| RUnboundValue of string
| RNotAFunction of value
| RDivisionByZero
| RTypeMismatch
| RInvalidOperand
| RIfCondNotBool
| RStepLimitExceeded
| REvalError
let pp_runtime_error fmt = function
| RUnboundValue x -> Format.fprintf fmt "Unbound value: %s" x
| RNotAFunction v -> Format.fprintf fmt "This is not a function: %s" (show_value v)
| RDivisionByZero -> Format.fprintf fmt "division by zero"
| RTypeMismatch -> Format.fprintf fmt "type mismatch"
| RInvalidOperand -> Format.fprintf fmt "operand type mismatch"
| RIfCondNotBool -> Format.fprintf fmt "condition must be bool"
| RStepLimitExceeded -> Format.fprintf fmt "step limit exceeded"
| REvalError -> Format.fprintf fmt "evaluation error"
;;
type 'a evalres =
| EFailed of runtime_error
| EOk of state * 'a
[@@deriving show]
let pp_value fmt = function
| VInt x -> Format.fprintf fmt "%d" x
| VFloat x -> Format.fprintf fmt "%f" x
| VBool x -> Format.fprintf fmt "%b" x
| VClosure _ -> Format.fprintf fmt "<fun>"
| VUnit -> Format.fprintf fmt "()"
;;
let pp_toplevel_value fmt = function
| VExpr v -> Format.fprintf fmt "- : %a" pp_value v
| VLet (x, v) -> Format.fprintf fmt "val %s = %a" x pp_value v
;;
let ( >>= ) m f st =
match m st with
| EFailed s -> EFailed s
| EOk (st', x) -> f x st'
;;
let ( let* ) = ( >>= )
let return x st = EOk (st, x)
let read st = EOk (st, st)
let write st (_ : state) = EOk (st, ())
let fail s _ = EFailed s
let run f st = f st
let step =
let* remaining_steps = read in
if remaining_steps <= 0 then fail RStepLimitExceeded else write (remaining_steps - 1)
;;
let lookup env x =
match Table.lookup x env with
| Some res -> return res
| None -> fail (RUnboundValue x)
;;
let make_closure env param body label = VClosure { param; body; env; label }
let rec eval env exp =
let* () = step in
match exp with
| EConst (IConst c) -> return (VInt c)
| EConst (FConst c) -> return (VFloat c)
| EConst (BConst c) -> return (VBool c)
| EVar x ->
let* v = lookup env x in
return v
| EBinOp (op, l, r) -> eval_binop env op l r
| EIf (cond, e1, e2) -> eval_if env cond e1 e2
| EFun (EVar x, e) -> return (make_closure env x e ENonrec)
| ELet (Nonrecursive, Bind (EVar x, e1), e2) ->
let* v1 = eval env e1 in
let env' = Table.extend x v1 env in
let* res = eval env' e2 in
return res
| ELet (Recursive, Bind (EVar x, e1), e2) ->
let* v1 = eval (Table.extend x VUnit env) e1 in
let v1' =
match v1 with
| VClosure { param; body; env; _ } -> VClosure { param; body; env; label = ERec x }
| v -> v
in
let env' = Table.extend x v1' env in
let* res = eval env' e2 in
return res
| EApp (e1, e2) ->
let* v1 = eval env e1 in
let* v2 = eval env e2 in
apply_closure v1 v2
| _ -> fail REvalError
and eval_binop env op e1 e2 =
let* v1 = eval env e1 in
let* v2 = eval env e2 in
let have_same_val_type l r =
match l, r with
| VBool _, VBool _ | VInt _, VInt _ | VFloat _, VFloat _ -> true
| _ -> false
in
match op, v1, v2 with
| Add, VInt l, VInt r -> return (VInt (l + r))
| Sub, VInt l, VInt r -> return (VInt (l - r))
| Mul, VInt l, VInt r -> return (VInt (l * r))
| Div, VInt l, VInt r -> if r = 0 then fail RDivisionByZero else return (VInt (l / r))
| AddF, VFloat l, VFloat r -> return (VFloat (l +. r))
| SubF, VFloat l, VFloat r -> return (VFloat (l -. r))
| MulF, VFloat l, VFloat r -> return (VFloat (l *. r))
| DivF, VFloat l, VFloat r ->
if r = 0. then fail RDivisionByZero else return (VFloat (l /. r))
| Eq, l, r when have_same_val_type l r -> return (VBool (l = r))
| Neq, l, r when have_same_val_type l r -> return (VBool (l <> r))
| Lt, l, r when have_same_val_type l r -> return (VBool (l < r))
| Leq, l, r when have_same_val_type l r -> return (VBool (l <= r))
| Gt, l, r when have_same_val_type l r -> return (VBool (l > r))
| Geq, l, r when have_same_val_type l r -> return (VBool (l >= r))
| And, VBool l, VBool r -> return (VBool (l && r))
| Or, VBool l, VBool r -> return (VBool (l || r))
| _ -> fail RInvalidOperand
and eval_if env cond e1 e2 =
let* () = step in
let* cond' = eval env cond in
match cond' with
| VBool true -> eval env e1
| VBool false -> eval env e2
| _ -> fail RIfCondNotBool
and apply_closure vfun varg =
let* () = step in
match vfun with
| VClosure { param; body; env; label = ENonrec } ->
let defenv' = Table.extend param varg env in
eval defenv' body
| VClosure { param; body; env; label = ERec x } ->
let defenv' = Table.extend param varg (Table.extend x vfun env) in
eval defenv' body
| _ -> fail (RNotAFunction vfun)
;;
let eval_toplevel env tl =
match tl with
| TopExpr e ->
let* v = eval env e in
return (env, VExpr v)
| TopLet (Nonrecursive, Bind (EVar x, e)) ->
let* v = eval env e in
let env' = Table.extend x v env in
return (env', VLet (x, v))
| TopLet (Recursive, Bind (EVar x, e)) ->
let env' = Table.extend x VUnit env in
let* v = eval env' e in
let v' =
match v with
| VClosure c -> VClosure { c with label = ERec x }
| _ -> v
in
let env'' = Table.extend x v' env in
return (env'', VLet (x, v'))
| _ -> fail REvalError
;;
let run_eval tl env steps = run (eval_toplevel env tl) steps