src/eval.ml

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open Lang

module Eval () = struct
  let tbl = Hashtbl.create 512

  let const = function
    | Literal l ->
        Const (Literal l)
    | Var x -> (
      try Hashtbl.find tbl x with Not_found -> Const (Var x) )

  let rec expr = function
    | Const c ->
        const c
    | Bind (x, e, e') ->
        let res = expr e in
        Hashtbl.add tbl x res ; expr e'
    | Abstract (b, p, e) ->
        Abstract (b, p, expr e)
    | Apply (e1, e2) -> (
        let e1' = expr e1 in
        let e2' = expr e2 in
        match e1' with
        | Abstract (_, p, e) -> (
          match e2' with
          | Const (Literal _) ->
              Hashtbl.add tbl p e2' ; expr e
          | Abstract _ ->
              Hashtbl.add tbl p e2' ; expr e
          | _ ->
              Apply (e1', e2') )
        | _ ->
            Apply (e1', e2') )
    | Match (origin, match_expr, cases) -> (
        let match_expr = expr match_expr in
        match match_expr with
        | Const (Literal match_litteral) -> (
            let res = ref None in
            List.iter
              (function
                | x, y when x = match_litteral -> res := Some y | _ -> ())
              cases ;
            (* TODO: add a check for exhaustiveness with proper error at some point and make this an internal error *)
            (* TODO: this could be a hashtbl instead of a list ? *)
            match !res with
            | None ->
                failwith "missing match case"
            | Some res ->
                expr res )
        | _ ->
            (* TODO: in this case, we're evaluating ("reducing") all cases, when we add effects, we shouldn't do that so brutally *)
            Match
              (origin, match_expr, List.map (fun (x, y) -> (x, expr y)) cases) )
    | Type (id, cons, e) ->
        Type (id, cons, expr e)
end