[Haskell-cafe] Using Template Haskell to make type-safe database
wss at Cs.Nott.AC.UK
Thu May 8 05:02:12 EDT 2008
> Not only pictures, but also code can say more than a thousands words.
> Therefore, I have been implementing a proof of concept. The code is
> attached in two files.
Nice! I have to admit, it's much nicer than I expected it to be. Just
out of curiousity, what happens when you write:
selectTupleList :: Connection -> IO [Integer]
selectTupleList :: Connection -> IO [(Integer, String, String)]
What kind of error message do you get? More specifically, is this
error caught statically or dynamically.
The only other limitation I can think of, would be in the situation
where you don't have compile-time access to the database, e.g.
developing software for a client with a database that can only be
accessed from their intranet. I have no idea how much of a limitation
> ok, there is some noise. But at the end of line three it says "Unknown
> column 'duser_id'". Also with a little more work I could properly
> improve the output.
The message is a bit verbose, but if you ignore the noise, it gives
pretty good feedback about what's wrong. Good.
>> Perhaps I should explain my own thoughts on the subject a bit better.
>> I got interested in this problem because I think it makes a nice
>> example of dependent types "in the real world" - you really want to
> But won't you end up implementing all the functionality of an SQL
> parser? While possible, it does seem like a huge job. With a TH
> you will safe a lot of work.
Yes - but parsing the result of an SQL describe statement is pretty
> A library that
> will be a lot more complex to learn than what I am proposing (assuming
> the developer already knows SQL).
Hmm. This is a rather sticky point. One might also argue that Haskell
developers have to learn SQL to use the solution you propose. I'm not
particularly convinced. Both approaches have their merits I think.
Anyhow - nice work! Have you asked Bjorn Bringert what he thinks? He's
a really clever and approachable guy - and he knows a lot more about
interfacing with databases than I do.
This message has been checked for viruses but the contents of an attachment
may still contain software viruses, which could damage your computer system:
you are advised to perform your own checks. Email communications with the
University of Nottingham may be monitored as permitted by UK legislation.
More information about the Haskell-Cafe