C# HList example

Extension.Npgsql.cs

using System;
using System.Linq.Expressions;
using ZeroORM.SqlBuilder.Vendor;

namespace ZeroORM.SqlBuilder
{
	public static class NpgsqlExtension
	{
		/// <summary>
		/// Single vendor in list overload
		/// </summary>
		public static TResult Npgsql<TExprBuilder, TResult>
		(
			this IVendorBuilder<TExprBuilder, Npgsql, UnknownReturnType> builder,
			Expression<Func<INpgsqlExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is the first
		/// </summary>
		public static IVendorBuilder<TExprBuilder, TNextVendor, TResult> Npgsql<TExprBuilder, TNextVendor, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<Npgsql, TNextVendor>, UnknownReturnType> builder,
			Expression<Func<INpgsqlExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			where TNextVendor : IZeroORMVendor
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is neither first nor last
		/// </summary>
		public static IVendorBuilder<TExprBuilder, TNextVendor, TResult> Npgsql<TExprBuilder, TNextVendor, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<Npgsql, TNextVendor>, TResult> builder,
			Expression<Func<INpgsqlExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			where TNextVendor : IZeroORMVendor
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is the last 
		/// </summary>
		public static TResult Npgsql<TExprBuilder, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<Npgsql, VendorsHListEnd>, TResult> builder,
			Expression<Func<INpgsqlExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			=> builder.Move( vendorExpression );
	}
}

Extension.TSql.cs

using System;
using System.Linq.Expressions;
using ZeroORM.SqlBuilder.Vendor;

namespace ZeroORM.SqlBuilder
{
	public static class TSqlExtension
	{
		/// <summary>
		/// Single vendor in list overload
		/// </summary>
		public static TResult TSql<TExprBuilder, TResult>
		(
			this IVendorBuilder<TExprBuilder, SqlServer, UnknownReturnType> builder,
			Expression<Func<ISqlServerExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is the first
		/// </summary>
		public static IVendorBuilder<TExprBuilder, TNextVendor, TResult> TSql<TExprBuilder, TNextVendor, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<SqlServer, TNextVendor>, UnknownReturnType> builder,
			Expression<Func<ISqlServerExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			where TNextVendor : IZeroORMVendor
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is neither first nor last
		/// </summary>
		public static IVendorBuilder<TExprBuilder, TNextVendor, TResult> TSql<TExprBuilder, TNextVendor, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<SqlServer, TNextVendor>, TResult> builder,
			Expression<Func<ISqlServerExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			where TNextVendor : IZeroORMVendor
			=> builder.Move( vendorExpression );

		/// <summary>
		/// Multiple vendors in list overload, case when current is the last 
		/// </summary>
		public static TResult TSql<TExprBuilder, TResult>
		(
			this IVendorBuilder<TExprBuilder, HLI<SqlServer, VendorsHListEnd>, TResult> builder,
			Expression<Func<ISqlServerExpressionBuilder<TExprBuilder>, TResult>> vendorExpression
		)
			where TExprBuilder : ISqlExpressionBuilder
			=> builder.Move( vendorExpression );
	}
}

IVendorBuilder.cs

namespace ZeroORM.SqlBuilder.Vendor
{
	public interface IVendorBuilder<TBuilder, TCurrent, TResult>
		where TCurrent : IZeroORMVendor
	{

	}
}

IVendorBuilderHListIterator.cs

using System;
using System.Linq.Expressions;

namespace ZeroORM.SqlBuilder.Vendor
{
	public static class IVendorBuilderExtensions
	{
		/// <summary>
		/// Single vendor in list overload
		/// </summary>
		public static TResult Move
		<
			TBuilder,
			TSingleVendor,
			TFirstVendorBuilder,
			TResult
		>
		(
			this IVendorBuilder<TBuilder, TSingleVendor, UnknownReturnType> _,
			Expression<Func<TFirstVendorBuilder, TResult>> vendorExpression
		)
			where TSingleVendor : IZeroORMVendor
			where TFirstVendorBuilder : IConcreteVendorBuilder<TBuilder, TSingleVendor>
			=> default;

		/// <summary>
		/// Multiple vendors in list overload, case when current is the first
		/// </summary>
		public static IVendorBuilder<TBuilder, TNextVendor, TResult> Move
		<
			TBuilder,
			TCurrentVendor,
			TNextVendor,
			TCurrentVendorBuilder,
			TResult
		>
		(
			this IVendorBuilder<TBuilder, HLI<TCurrentVendor, TNextVendor>, UnknownReturnType> _,
			Expression<Func<TCurrentVendorBuilder, TResult>> vendorExpression
		)
			where TCurrentVendor : IZeroORMVendor
			where TNextVendor : IZeroORMVendor
			where TCurrentVendorBuilder : IConcreteVendorBuilder<TBuilder, TCurrentVendor>
			=> default;

		/// <summary>
		/// Multiple vendors in list overload, case when current is neither first nor last
		/// </summary>
		public static IVendorBuilder<TBuilder, TNextVendor, TResult> Move
		<
			TBuilder,
			TCurrentVendor,
			TNextVendor,
			TCurrentVendorBuilder,
			TResult
		>
		(
			this IVendorBuilder<TBuilder, HLI<TCurrentVendor, TNextVendor>, TResult> _,
			Expression<Func<TCurrentVendorBuilder, TResult>> vendorExpression
		)
			where TCurrentVendor : IZeroORMVendor
			where TNextVendor : IZeroORMVendor
			where TCurrentVendorBuilder : IConcreteVendorBuilder<TBuilder, TCurrentVendor>
			=> default;

		/// <summary>
		/// Multiple vendors in list overload, case when current is the last 
		/// </summary>
		public static TResult Move
		<
			TBuilder,
			TCurrentVendor,
			TCurrentVendorBuilder,
			TResult
		>
		(
			this IVendorBuilder<TBuilder, HLI<TCurrentVendor, VendorsHListEnd>, TResult> _,
			Expression<Func<TCurrentVendorBuilder, TResult>> vendorExpression
		)
			where TCurrentVendor : IZeroORMVendor
			where TCurrentVendorBuilder : IConcreteVendorBuilder<TBuilder, TCurrentVendor>
			=> default;
	}
}

IZeroORMVendorList.cs

namespace ZeroORM.SqlBuilder
{
	public interface IZeroORMVendorList
	{

	}
	public interface IZeroORMVendorList<TProvider1> : IZeroORMVendorList
		where TProvider1 : IZeroORMVendor
	{

	}

	public class VendorsHListEnd : IZeroORMVendor
	{

	}

	/// <summary>
	/// Stands for Heterogeneous List Item. Long name for such a thing reduces readability significially, so it is abbreviated.
	/// </summary>
	public class HLI<T1, T2> : IZeroORMVendor
		where T1 : IZeroORMVendor
		where T2 : IZeroORMVendor
	{

	}
}

Npgsql.cs

using System;
using ZeroORM.SqlBuilder.Vendor;

namespace ZeroORM.SqlBuilder
{
	public class Npgsql : IZeroORMVendor { }

	public interface INpgsqlExpressionBuilder<TExprBuilder> : IConcreteVendorBuilder<TExprBuilder, Npgsql>
		where TExprBuilder : ISqlExpressionBuilder
	{
		DateTime CurrentTimestamp { get; }
	}
}

SqlServer.cs

using System;
using ZeroORM.SqlBuilder.Vendor;

namespace ZeroORM.SqlBuilder
{
	public class SqlServer : IZeroORMVendor
	{
	}

	public interface ISqlServerExpressionBuilder<TExprBuilder> : IConcreteVendorBuilder<TExprBuilder, SqlServer>
		where TExprBuilder : ISqlExpressionBuilder
	{
		DateTime GetDate();
	}
}

UsageExample.cs

DateTime x = db
	.Vendor()
	.Npgsql( npg => npg.CurrentTimestamp )
	.TSql( tsql => tsql.GetDate() )