John Ky <newho...@gmail.com> wrote in article
<bd4fcb030901181744i2b26172bv2328974ff911f...@mail.gmail.com> in
gmane.comp.lang.haskell.cafe:
> data Person = Person { name :: String, ... }
> data Business = Business { business_number :: Int, ...}
>
> key person = name person
> key business = business_number business
Let's make this concrete:
data Person = Person { name :: String, age :: Integer }
data Business = Business { business_number :: Int, revenue :: Double }
key person = name person
key business = business_number business
Even without dependent types, you can do the following (but of course,
you lose some syntactic sugar for records):
data Individual k v = Individual { key :: k, value :: v }
type Person = Individual String Integer
type Business = Individual Int Double
name :: Person -> String
name = key
age :: Person -> Integer
age = value
business_number :: Business -> Int
business_number = key
revenue :: Business -> Double
revenue = value
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