private Maybe<ResultSingle> VisitStmt(QueryParser.StatementContext context)
{
var results = new QueryVisitor(_zmi).Visit(context).Sequence();
if (results.HasNothing)
return Maybe<ResultSingle>.Nothing;
if (results.Val.Count != 1)
throw new ArgumentException("Nested queries must SELECT exactly one item.");
return new ResultSingle(results.Val.First().Value).Just();
}
/// <summary>
/// Visit a parse tree produced by <see cref="QueryParser.statement"/>.
/// <para>
/// The default implementation returns the result of calling <see cref="AbstractParseTreeVisitor{Result}.VisitChildren(IRuleNode)"/>
/// on <paramref name="context"/>.
/// </para>
/// </summary>
/// <param name="context">The parse tree.</param>
/// <return>The visitor result.</return>
public virtual Result VisitStatement([NotNull] QueryParser.StatementContext context)
{
return(VisitChildren(context));
}
