From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: Victor Porton Newsgroups: comp.lang.ada Subject: Re: Indefinite type while writing a recursive descent parser Date: Thu, 02 Nov 2017 21:39 +0200 Organization: Aioe.org NNTP Server Message-ID: References: NNTP-Posting-Host: AXbaCSC1gsQOwLBV12d/+A.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Complaints-To: abuse@aioe.org User-Agent: KNode/4.14.10 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:48711 Date: 2017-11-02T21:39:00+02:00 List-Id: Victor Porton wrote: > Victor Porton wrote: > >> Victor Porton wrote: >> >>> I am writing a recursive descent parser. (It parses RDF relations rather >>> than a text file, but that's not very important for my question, except >>> for the fact that I cannot use an existing text parser package.) >>> >>> While parsing I need to extract data (numbers, booleans, arrays, etc.) >>> >>> My first idea was: >>> >>> generic >>> type Data_Type(<>) is private; >>> package Base_Predicate is >>> type Base_Predicate_Parser is tagged >>> record >>> Predicate: URI_Type; >>> Data: access Data_Type; >>> end record; >>> not overriding >>> procedure Parse (Parser: Base_Predicate_Parser; Node: Node_Type) is >>> null; >>> end Base_Predicate; >>> >>> I wanted my node parsers to assign to Data.all if Data/=null. >>> >>> But then I realized that this won't work for an indefinite Data_Type. >>> >>> So I have an Ada (2012) specific issue on possible ways to assign data >>> while parsing. Please give advice. >>> >>> I could use Indefinite_Holders everywhere but this would be a step into >>> the direction of being like a dynamic language instead of strong typing >>> system which Ada offers. I don't like to make a step in this direction. >> >> It seems for me the right idea to: >> >> - restrict Data_Type only to definite types as a record member where we >> are to store the data is anyway not supporting indefinite types >> >> - whenever we need an indefinite type, replace it with an indefinite >> holder defined specifically for this type > > However, this seems a suboptimal solution for lists of indefinite objects: > this way of work would lead to a definite vector of indefinite holders > rather than to indefinite vector of indefinite objects. Oh, it seems I know what to do: When parsing data into a vector, for each element first parse into an indefinite holder and then add a copy of it to the end of the (indefinite) vector. -- Victor Porton - http://portonvictor.org