Question

Is it possible in haskell to match complex patterns?

I mean, I have a Comma Separater Values (CSV) file:

name,ID,fieldA,fieldB

is it possible to write a function like:

getName (n:',':xs) = n

where n is not a single element but a list?

Answer 1

You should write a function to split your line…

import Data.List

parts = map tail . groupBy (/=) . (',':)

Then you can write your accessor functions easily:

getName xs = n where [n,_,_,_] = parts xs
getID   xs = i where [_,i,_,_] = parts xs
...

But as always it would be nice to use a data type:

data Record = Record {getName :: String   
                     ,getId :: Int
                     ,getFieldA  
                     ,getFieldB :: String
                     } deriving Show 

initRecord xs = Record name (read id) fieldA fieldB where
                [name, id, fieldA, fieldB] = parts xs

Of course, if you need error handling, it gets a little bit more difficult…

BTW, there is a Haskell CSV lib out there: http://hackage.haskell.org/packages/archive/csv/0.1.1/doc/html/Text-CSV.html