A Simple Sentence Parser

    Determine if a simple sentence is grammatically correct.
    The sentence uses the following BNF:

        <sentence> ::= <verb><direct-object>[<indirect-object>]
        <direct-object> ::= [<determiner>]<adjective>*<noun>
        <indirect-object> ::= <preposition><direct-object>
        <determiner> ::= a | an | the
        <adjective> ::= red | shiny | heavy
        <noun> ::= ball | wrench | gun | pliers
        <preposition> ::= with | in | at
        <verb> ::= get | throw | shoot

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