[Haskell-beginners] pattern matching on a common element

[Daniel Trstenjak]

Hi Rahul,

On Fri, Nov 25, 2016 at 12:06:06PM +0530, Rahul Muttineni wrote:
> data X =
>   A1 { name :: String, d :: Double}
> | A2 { name :: String, i :: Int}
> | A3 { name :: String, d1 :: Double, i1 :: Int}
> 
> Now you can use `name` directly to get the string component of the different
> variants.

It's not recommended to mix record syntax and ADTs, because you
can get runtime errors that the compiler can't catch during compile
time, like calling:

   i (A1 "foo" 3.2)

If you're having the same field in all variants, then an
other approach might be better:

   data A = Ai Int | Ad Double | Aid Int Double

   data X = X { name :: String, a :: A }

Greetings,
Daniel