| | |
Summary: Sized (Co-)Inductive Types
With Applications to Generic Programming
Andreas Abel
ProgLog Seminar, April 5, 2006
1 Example: Generic Finite Maps
Finite Maps for List-shaped Keys
· Key type: [a], value type: v
data MapList f v
= Leaf
| Node (Maybe v) (f (MapList f v))
· If f w = a fin w, then MapList f v = [a] fin v.
· Looking up a list-shaped key:
lookupList :: (forall w. a -> f w -> Maybe w) ->
[a] -> MapList f v -> Maybe v
lookupList lo l Leaf = Nothing
lookupList lo [] (Node mv m) = mv
lookupList lo (a:as) (Node mv m)
= lo a m >>= lookupList as
Merging Finite Maps
· Merging (possibly undefined) values.
|
