2 points about language
Alastair David Reid
24 Aug 2001 12:32:02 -0600
> Rewriting (x++y)++z to x++(y++z) so one, for example, doesn't need
> all the kludge in the Pretty printer?
Note that the "kludge" in the pretty-printer is primarily to handle
cases where the ++'s do not occur next to each other in the static text.
For example, I might glue together a tree of strings using code like this:
data Tree a = Node a [Tree a]
glue :: Tree String -> String
glue (Node x ts) = x ++ concatMap glue ts
The uses of ++ and concatMap look just fine - at each node I'm
appending strings in the efficient right-associative manner. But my
code still takes quadratic time (worst case) because the ++ gets
repeated at each level in the tree.
I think this is the real problem being fixed in Pretty, ShowS, etc.
Alastair Reid [email protected] http://www.cs.utah.edu/~reid/