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Diffstat (limited to 'utils/mkUserGuidePart/DList.hs')
| -rw-r--r-- | utils/mkUserGuidePart/DList.hs | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/utils/mkUserGuidePart/DList.hs b/utils/mkUserGuidePart/DList.hs new file mode 100644 index 0000000000..c4b9283e52 --- /dev/null +++ b/utils/mkUserGuidePart/DList.hs @@ -0,0 +1,13 @@ +module DList where + +newtype DList a = DList ([a] -> [a]) + +snoc :: DList a -> a -> DList a +DList f `snoc` x = DList (f . (x:)) + +toList :: DList a -> [a] +toList (DList f) = f [] + +instance Monoid (DList a) where + mempty = DList id + DList a `mappend` DList b = DList (a . b) |