ocamlyacc and polymorphic variants

From: Markus Mottl (mottl@miss.wu-wien.ac.at)
Date: Sat Jan 08 2000 - 19:38:45 MET

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    Hello,

    I have just tried in how far it is possible to use ocamlyacc together with
    polymorphic variants. As it seems, this is a somewhat dangerous
    combination, because ocamlyacc-generated code requires Obj.magic internally
    to cast values to the appropriate type.

    I am not sure in which order the data constructors are generated, i.e. what
    internal representation the polymorphic variants get. I thought that they
    would be generated in order of appearance, but when I implemented the
    parser, the code behaved more than strangely, namely differently for byte-
    and native code. This is an indication that the returned values do not
    fully correspond to the type they are supposed to be of, possibly because
    the internal tags of the data constructors are not in the right order.

    The result type enumerated the data constructors exactly in the same order
    as they appeared in the parser specification, but this does not seem to
    work.

    Is it possible at all to return polymorphic variants from the parser? If
    yes, how do I have to specify the return type?

    A workaround would be to not use polymorphic variants in the parser and to
    use a conversion function outside to convert the "normal" into polymorphic
    ones.

    Regards,
    Markus Mottl

    -- 
    Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl
    



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