[Haskell-cafe] Applying different functions to different types for
szekeres at iii.hu
Thu Jul 16 17:15:20 EDT 2009
I want to build a framework to apply different functions to different types
of lists and I want to generalize the solution as much as possible but my
Haskell knowledge is not really enough to do this (I'm a haskell novice).
The problem has two dimensions:
1. Lets say I have two functions:
r13, ul : Char -> Char
where r13 returns the rot13ed character, and ul converts upper case chars to
lower case and vice versa. Later I want a rot13 function that can operate on
different types of lists and an uxl function that can also operate on
different types of lists.
2. Lets say I have two kinds of lists to handle: String and
Data.ByteString.Lazy as L.
For Strings I want the updater function to be used for each character and
for L I want all items to be converted to Char, the updater function to be
updated and the result to be converted back to the original item type.
Therefore I define a common class for handling these lists:
class ListUpdater a where
updateFn :: Char -> Char
update :: a -> a
so I can define the update function for the different types of lists:
instance ListUpdater String where
update = map updateFn
instance ListUpdater L.ByteString where
update = L.pack . (map updateFn) . L.unpack
But now how should I glue these 2 dimensions together? How to say that I
want a rot13 function that applies to any data type instantiated from
ListUpdater and that is using the r13 function to do the update? And also
that I want an uxl function that also applies to any data type instantiated
from ListUpdater and that is using the ul function to do the update?
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe