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)); }