Hello,
thinking about whether the pretty printer proposed by Wadler requires
some changes to be efficient in a strict language, I stumbled over the
the last case defining `flatten':
flatten (x :<|> y) = flatten x
I wonder why it is necessary here to recurse on x. The only point were a
doc (x:<|>y) is constructed is in the function `group':
group z = flatten z :<|> z
So the x above is always flat already. Wouldn't the equation
flatten (x :<|> y) = x
suffice? Doing recursion here seems to be unnecessary overhead. In
particular, it prevents structure sharing between alternatives when
grouping, because flatten rebuilds the whole doc tree (which might be
more of a problem without laziness).
Am I missing something?
- Andreas
