digraph G {
    REPL             -> Parser;
    REPL             -> Evaluator;
    Parser           -> Lexical_Analyzer
    Parser           -> Abstract_Syntax;
    Parser           -> Values;
    Evaluator        -> Abstract_Syntax;
    Evaluator        -> Environments;
    Evaluator        -> Values;
    Lexical_Analyzer -> Values;
    Abstract_Syntax  -> Values;
    Environments     -> Values;
}