Re: [Haskell-beginners] Record types with multiple constructors

7 Dec 2014


      On Sun, Dec 07, 2014 at 09:37:11AM +0000, Derek McLoughlin 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?
I think you might see it fairly frequently in users of command line
parser libs, e.g. optparse-applicative[^1], for accepting
sub-commands.

/M

[^1]: http://hackage.haskell.org/package/optparse-applicative

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Magnus Therning                      OpenPGP: 0xAB4DFBA4 
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