20 lines
663 B
OCaml
20 lines
663 B
OCaml
open Ppxlib
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let expand ~ctxt env_var =
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let loc = Expansion_context.Extension.extension_point_loc ctxt in
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match Sys.getenv env_var with
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| value -> Ast_builder.Default.estring ~loc value
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| exception Not_found ->
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let ext =
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Location.error_extensionf ~loc "The environement variable %s is unbound"
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env_var
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in
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Ast_builder.Default.pexp_extension ~loc ext
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let my_extension =
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Extension.V3.declare "get_env" Extension.Context.expression
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Ast_pattern.(single_expr_payload (estring __))
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expand
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let rule = Ppxlib.Context_free.Rule.extension my_extension
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let () = Driver.register_transformation ~rules:[ rule ] "get_env"
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