44 lines
1.3 KiB
OCaml
44 lines
1.3 KiB
OCaml
type id = string
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type ty_annot = id * Types.ty
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type lam =
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Fun of ty_annot * lam
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| App of lam * lam
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| Var of id
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| Exf of lam * Types.ty
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(** alpha renaming in a deterministic way *)
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let alpha_convert (e : lam) : lam =
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let cpt_ty = ref 0 in (* id cpt for type variables *)
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let cpt_var = ref 0 in (* id cpt for variables *)
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let generator (cpt : int ref) : id = (* id generator *)
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let v = string_of_int !cpt
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in incr cpt; v
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in let renamed = ref []
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in let rename (cpt : int ref) (var : id) : id = (* checks if a variable already has a new id, or generates one *)
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match List.assoc_opt var !renamed with
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| Some var' -> var'
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| None -> let var' = generator cpt in (
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renamed := (var, var')::!renamed;
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var')
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in let rec alpha_ty (t : Types.ty) : Types.ty = match t with
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Arr (t1, t2) -> Arr (alpha_ty t1, alpha_ty t2)
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| TVar (v) -> TVar (rename cpt_ty v)
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| Bot -> Bot
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in let rec alpha_aux (e : lam) : lam = match e with (* actual renaming *)
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Fun ((v, t), e) -> Fun ((rename cpt_var v, alpha_ty t), alpha_aux e)
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| App (e1, e2) -> App (alpha_aux e1, alpha_aux e2)
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| Var v -> Var (rename cpt_var v)
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| Exf (e, s) -> Exf (alpha_aux e, s)
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in alpha_aux e
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(** alpha equivalence *)
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let (=~) (e1 : lam) (e2 : lam) : bool =
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alpha_convert e1 = alpha_convert e2
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