Re: [Haskell-beginners] How to "add column" to a Table?

26 Apr 2015


      On 04/26/2015 06:13 AM, martin wrote:
...
Hello all,
I suppose the natural representation for a Table is a List of Tuples. Or more generally I'll probably end up with a type
"Table a" where a stands for the Columns.
I cannot figure out how to add a new Column to a Table. What would be the type of such an operation? If I just want to
add an empty Column (which what an RDBMS would do), would I do something like this?
addColumn :: ColumnDef -> Table a -> Table b
But what is this ColumnDef? It would need to contain the name and type of the new column. To implement this operation I
would have to somewehre add a column to something. But what is the type of this something. I don't see how I can add a
component to a Tuple in a generic way, or can I?
type Person = ( Int,    -- ID
                String, -- Name
                Int,    -- Age
                Bool    -- Evil bit
              )

type Place = ( Int,    -- ID
               String, -- Name
               Double, -- Longitude
               Double, -- Latitude
               Double  -- Elevation
             )

data Column = Person | Place

type Table = [Column]

addColumn :: Table -> Column -> Table
addColumn table col = table ++ [col]

Re: [Haskell-beginners] How to "add column" to a Table?

Michael Orlitzky