34 lines
1,007 B
OCaml
34 lines
1,007 B
OCaml
open Ppxlib
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let existential ~loc =
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let lident = { loc; txt = Longident.parse "Constructor" } in
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let pattern =
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{
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ppat_loc = loc;
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ppat_loc_stack = [];
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ppat_attributes = [];
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ppat_desc =
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Ppat_construct (lident, Some ([ { loc; txt = "a" } ], [%pat? _]));
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}
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in
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[%stri let f x = match x with [%p pattern] -> ()]
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let named_existential =
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Context_free.Rule.extension
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(Extension.V3.declare "named_existentials" Extension.Context.structure_item
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Ast_pattern.(pstr nil)
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(fun ~ctxt ->
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let loc = Expansion_context.Extension.extension_point_loc ctxt in
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existential ~loc))
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let () =
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Driver.V2.register_transformation ~rules:[ named_existential ]
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"named_existentials"
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let str_type_decl =
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Deriving.Generator.V2.make_noarg (fun ~ctxt _type_decl ->
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let loc = Expansion_context.Deriver.derived_item_loc ctxt in
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[ existential ~loc ])
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let _ = Deriving.add ~str_type_decl "named_existentials"
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let () = Driver.standalone ()
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