Short list with things to finish for D2

[yigal chripun]

aarti_pl Wrote:

> Walter Bright pisze:
> > Don wrote:
> >> There's not many sensible operators anyway. opPow is the only missing 
> >> one that's present in many other general-purpose languages. The only 
> >> other ones I think are remotely interesting are dot and cross product.
> > 
> > Yup.
> > 
> >> Anything beyond that, you generally want a full DSL, probably with 
> >> different precendence and associativity rules. Eg, for regexp, you'd 
> >> want postfix * and + operators. There are examples of clever things 
> >> done in C++  with operator overloading, but I think that's just 
> >> because it's the only way to do DSLs in C++.
> > 
> > I was enthralled with the way C++ did it for regex for a while, but when 
> > I think more about it, it's just too clever. I think it's more operator 
> > overloading abuse now.
> > 
> >> I don't think the applications are there.
> > 
> > I agree.
> 
> Well, I can understand your fear about operator abuse. And I agree that 
> code might be awful when operator overloading will be abused.
> 
> But I have in mind one very convincing example. I defined in D/Java SQL 
> syntax. They are also other frameworks which do the same.
> 
> What can I say about my experiences with using such framework: it is 
> very, very powerful concept. It cuts time necessary to develop 
> application, makes sql statements type safe and allows to pass around 
> parts of sql statements inside application. It also makes easy 
> refactoring of sql statement (especially in Java). Its huge win 
> comparing it to defining DSL as strings.
> 
> It's hard to explain just in few sentences all details. I have already 
> done it long time ago, and in my first post I provided links.
> 
> Problem with current approach is that I have to define SQL in D/Java in 
> following way:
> 
> auto statement = Select(visitcars.name).Where(And(More(visitcards.id, 
> 100), Like(visitcards.surname, "A*")));
> 
> Please look at code in Where(). It's so awfuuuuulllllll!
> 
> It would be so much better to write:
> auto statement = Select(visitcars.name).Where((visitcards.id `>` 100) 
> `AND` (visitcards.surname `Like` "A*"));
> 
> I used here syntax which you have proposed with delimiter ``. I think it 
> is good enough solution for such purpose.
> 
> But please, don't underestimate problem! Many DSL languages would never 
> appear if languages would be good enough.
> 
> As I said solution with delimiter is good enough for me. It has another 
> advantage that it clearly shows in code that you have overloaded 
> operator here, so no surprises here. Additionally when you implement 
> template function:
> opInfix('AND')(val0, val1);
> you pass string into template. So I see it quite intuitive that you use 
> string as operator: ``. Maybe there will be not necessary to change 
> current behavior that `` defines string.
> 
> I think we have good possibility to  open this door now. It can be even 
> implemented later, but I would wish just not to close this door now :-)
> 
> BR
> Marcin Kuszczak
> (aarti_pl)

There's nothing more hideous than all those frameworks in Java/C++ that try to re-enginer SQL into functions, templates, LINQ, whatever.
SQL *is* a perfectly designed language for its purpose and it doesn't need to be redisnged! The only problem with this is the type-safety when embedding sql as string in a host language. 
the solution is two-phased: 

phase a is simple, look at the C# API for postgres (I think). The query is one string like:
"select * from table where :a > 42", the :name is a place holder for the host-language variable, and you call an API to bind those :names to variables in a type-safe way. the downside is that it's verbose. 
 
phase b is what Nemerle does with the above - it has an AST macro to wrap the above so you can write your query directly and it is checked as compile-time. 

No operators were abused in implementing this.