[Haskell-cafe] Substitute for records?
bringert at cs.chalmers.se
Mon Apr 10 16:18:29 EDT 2006
Mattias Bengtsson wrote:
> Currently i'm working, together with a friend, on an abstraction (sort
> of) of HaskellDB for a school-project.
> Basically we are generating haskell-modules similar to those generated
> by DBDirect in HaskellDB together with some helpers for the most common
> queries you'd want to run.
> HaskellDB has its own record system (HDBRec) and a HaskellDB-query also
> returns such a record. The accessor-functions for these records can
> later be found in DatabaseName.TableName.ColumnName.column. These should
> be imported qualified to avoid name clashes.
> This is some example code:
> students <- School.Students.all db
> mapM_ printStudentId students
> printStudentId rec = print $ rec!School.Students.Id.column
> The main problem for me here is this part:
> where i would rather just write
> This isn't possible and the other way is just too messy for my taste. It
> simply isn't the easy and nice syntax i had hoped for when we started to
> develop this.
> Are there any other nice substitutes for HDBRec or normal haskell
> records that i could use that doesn't make name clashes an issue?
It's not perfect, but you can make it a lot shorter by importing the
modules that declare the fields with shorter names:
import qualified School.Students as Students
import qualified School.Students.Name as Name
students <- Students.all db
mapM_ printStudentId students
printStudentId rec = print $ rec!Name.column
But the right answer, I'm afraid, is that there is no really nice way to
work with records in today's Haskell.
You may want to have a look at HList  to see if that works better. If
it does, you are very welcome to port HaskellDB to use it instead of HDBRec.
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