69 lines
2.0 KiB
OCaml
69 lines
2.0 KiB
OCaml
open Format;
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module S = Set.Make String;
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type term =
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[ Lambda of string and term
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| Atom of string
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| App of term and term
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| Opt of term and option term and term
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];
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value free_vars =
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let rec fv t env free =
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match t with
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[ Lambda x t -> fv t (S.add x env) free
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| Atom x -> if S.mem x env then free else S.add x free
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| App t1 t2 -> fv t1 env (fv t2 env free)
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| Opt _ _ _ -> assert False ]
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in fun t -> fv t S.empty S.empty;
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value print_set f s = do {
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fprintf f "@[<2>{ ";
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S.iter (fprintf f "%s@ ") s;
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fprintf f "}@]";
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};
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value t1 = Lambda "x" (App (Lambda "y" (App (Atom "y") (Atom "x"))) (Lambda "x" (Atom "x")));
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value t2 = Lambda "x" (App (Lambda "y" (App (Atom "y") (Atom "x"))) (Lambda "z" (Atom "z")));
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value t3 = Lambda "x" (App (Lambda "y" (App (Atom "y") (Atom "x"))) (Lambda "x" (Atom "z")));
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value t4 = Lambda "a" (App (Lambda "y" (App (Atom "y") (Atom "x"))) (Lambda "x" (Atom "z")));
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printf "t1: %a@." print_set (free_vars t1);
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printf "t2: %a@." print_set (free_vars t2);
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printf "t3: %a@." print_set (free_vars t3);
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printf "t4: %a@." print_set (free_vars t4);
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class fold ['accu] init =
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object (o : 'self_type)
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value accu : 'accu = init;
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method accu = accu;
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method term t =
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match t with
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[ Lambda x t -> (o#string x)#term t
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| Atom x -> o#string x
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| App t1 t2 -> (o#term t1)#term t2
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| Opt t1 ot t2 -> ((o#term t1)#option (fun o -> o#term) ot)#term t2 ];
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method string : string -> 'self_type = fun _ -> o;
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method option : ! 'a. ('self_type -> 'a -> 'self_type) -> option 'a -> 'self_type =
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fun f opt ->
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match opt with
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[ None -> o
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| Some x -> f o x ];
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end;
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class fold_atoms ['accu] f init =
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object (o : 'self_type)
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inherit fold ['accu] init as super;
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method term t =
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match t with
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[ Atom x -> {< accu = f x accu >}
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| _ -> super#term t ];
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end;
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value t5 = Opt (Atom "a") (Some (Atom "b")) (Atom "c");
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value atoms = ((new fold_atoms S.add S.empty)#term t5)#accu;
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printf "atoms: %a@." print_set atoms;
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