Yes: it becomes really easy to write partial/broken programs, e.g.: let myEmployee = RegularEmployee "Alice" ... supervisor = myEmployee { salesTarget = 5.4 } If you want to have both multiple constructors *and* multiple fields per constructor, I'd recommend one of the following: 1. Don't name the fields. 2. Use another type in between that has only one constructor, e.g. `data Supervisor = Supervisor { name :: String, salesTarget :: Double }`. A great example of this is the Node datatype[1] from xml-types. [1] http://www.stackage.org/haddock/2014-11-27-ghc78-exc-1/xml-types-0.3.4/Data-... On Sun Dec 07 2014 at 11:37:16 AM Derek McLoughlin < derek.mcloughlin@gmail.com> wrote:
Hi,
Record types usually have a single constructor. I've even seen blog posts that suggest that they must have a single constructor. However, multiple constructors are allowed:
data Employee = RegularEmployee { name :: String } | Supervisor { name :: String, salesTarget :: Double } Manager { name :: String, salesTarget :: Double budget :: Double }
I don't see this used much in Haskell code - either in explanatory books/tutorials or in code I've examined on GitHub. Are there drawbacks to using multiple constructors in this way?
Derek. _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners