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open Bwd
open Bwd.Infix
module S = Syntax
module D = Domain
module Internal =
struct
module Eff = Algaeff.Reader.Make (struct type nonrec t = D.env end)
let make_clos body = D.Clos { body; env = Eff.read() }
let rec inst_clos (D.Clos { body; env }) arg =
let env = env <: arg in
Eff.run ~env @@ fun () -> eval body
and app v w = match v with
| D.Lam clos -> inst_clos clos w
| D.Neutral (hd, frms) -> D.Neutral (hd, frms <: D.App w)
| _ -> invalid_arg "Eval.app"
and fst = function
| D.Pair (v, _) -> v
| D.Neutral (hd, frms) -> D.Neutral (hd, frms <: D.Fst)
| _ -> invalid_arg "Eval.fst"
and snd = function
| D.Pair (_, v) -> v
| D.Neutral (hd, frms) -> D.Neutral (hd, frms <: D.Snd)
| _ -> invalid_arg "Eval.snd"
and bool_elim cmot vtrue vfalse = function
| D.True -> vtrue
| D.False -> vfalse
| D.Neutral (hd, frms) -> D.Neutral (hd, frms <: D.BoolElim { cmot; vtrue; vfalse })
| _ -> invalid_arg "Eval.bool_elim"
and eval = function
| S.Var i -> BwdLabels.nth (Eff.read()) i
| S.Pi (base, fam) -> D.Pi (eval base, make_clos fam)
| S.Lam body -> D.Lam (make_clos body)
| S.App (a, b) -> app (eval a) (eval b)
| S.Sg (base, fam) -> D.Sg (eval base, make_clos fam)
| S.Pair (a, b) -> D.Pair (eval a, eval b)
| S.Fst a -> fst (eval a)
| S.Snd a -> snd (eval a)
| S.Type -> D.Type
| S.Bool -> D.Bool
| S.True -> D.True
| S.False -> D.False
| S.BoolElim { motive; true_case; false_case; scrut } ->
bool_elim (make_clos motive) (eval true_case) (eval false_case) (eval scrut)
end
let eval ~env tm = Internal.Eff.run ~env (fun () -> Internal.eval tm)
|