127 lines
3.5 KiB
OCaml
127 lines
3.5 KiB
OCaml
[@@@ocamlformat "disable"]
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open Ppxlib
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(* Simple demo without [as__] and [drop] *)
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let ___1 =
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let loc = Location.none in
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let ast = [%expr List.length xs = 0] in
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let pat =
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let open Ast_pattern in
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let length () =
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pexp_apply
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(pexp_ident (ldot (lident (string "List")) (string "length")))
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((nolabel ** __) ^:: nil)
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in
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let zero () = pexp_constant (pconst_integer (string "0") none) in
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pexp_apply
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(pexp_ident (lident (string "=")))
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((nolabel ** length ()) ^:: (nolabel ** zero ()) ^:: nil)
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in
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Ast_pattern.parse pat loc ast
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~on_error:(fun () -> "Error")
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(fun _length_argument -> "Success. As expected")
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[%%expect{|
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val ___1 : string = "Success. As expected"
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|}]
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(* We could use [as__] to capture whole [List.length ...] expression,
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and use [drop] to ignore length's argument *)
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let ___2 =
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let loc = Location.none in
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let ast = [%expr List.length xs = 0] in
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let pat =
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let open Ast_pattern in
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let length () =
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as__
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(pexp_apply
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(pexp_ident (ldot (lident (string "List")) (string "length")))
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((nolabel ** drop) ^:: nil))
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in
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let zero () = as__ (pexp_constant (pconst_integer (string "0") none)) in
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pexp_apply
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(pexp_ident (lident (string "=")))
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((nolabel ** length ()) ^:: (nolabel ** zero ()) ^:: nil)
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in
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Ast_pattern.parse pat loc ast
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~on_error:(fun () -> "error")
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(fun l r ->
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Format.asprintf "Success with '%a' and '%a'. As expected" Pprintast.expression l Pprintast.expression r
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)
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[%%expect{|
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val ___2 : string = "Success with 'List.length xs' and '0'. As expected"
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|}]
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(* Pitfall. If we forget unit argument and will use [as__], the success case
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will be fired before the error case. *)
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let ___3 =
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let loc = Location.none in
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let ast = [%expr 1] in
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let pat () =
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let open Ast_pattern in
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as__ (pexp_constant (pconst_integer (string "0") none))
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in
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let rez = Buffer.create 100 in
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Ast_pattern.parse (pat ()) loc ast
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~on_error:(fun () -> Printf.bprintf rez "An error")
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(fun zero_expr -> Buffer.add_string rez
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(Format.asprintf "Successfully got '%a' but error right after that (NOT EXPECTED). " Pprintast.expression zero_expr));
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Buffer.contents rez
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[%%expect{|
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val ___3 : string =
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"Successfully got '1' but error right after that (NOT EXPECTED). An error"
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|}]
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(* To avoid the pitfall above we could add extra () to delay evaluation *)
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let ___4 =
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let loc = Location.none in
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let ast = [%expr 1] in
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let pat () =
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let open Ast_pattern in
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as__ (pexp_constant (pconst_integer (string "0") none))
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in
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Ast_pattern.parse (pat ()) loc ast
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~on_error:(fun () () -> "Error, as expected")
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(fun _zero_expr () -> "Success and error after that\n%!")
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()
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[%%expect{|
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val ___4 : string = "Error, as expected"
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|}]
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(* But this pitfall is not introduced by [as__], it existed before too. *)
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let ___5 =
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let loc = Location.none in
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let ast = [%expr string_of_int 43] in
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let pat =
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let open Ast_pattern in
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pexp_apply
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(pexp_ident (lident __))
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((nolabel ** eint (int 42)) ^::
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(nolabel ** (pexp_ident (lident __))) ^::
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nil)
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in
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let b = Buffer.create 10 in
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let () = Ast_pattern.parse pat loc ast
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~on_error:(fun () -> Buffer.add_string b "It's an error")
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(fun s ->
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Printf.bprintf b "Partial success with '%s', but actually not, because... " s;
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(fun _ -> Printf.bprintf b "no, it's total success"))
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in
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Buffer.contents b
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[%%expect{|
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val ___5 : string =
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"Partial success with 'string_of_int', but actually not, because... It's an error"
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|}]
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