[Haskell-cafe] Re: Knot tying vs monads
John D. Ramsdell
ramsdell0 at gmail.com
Mon Nov 19 07:30:20 EST 2007
On Nov 17, 2007 3:04 PM, apfelmus <apfelmus at quantentunnel.de> wrote:
> Unfortunately, I don't have Paulson's book (or any other ML book :) at
> home. I'm too lazy to figure out the specification from the source code,
I guess the code is too opaque, as my colleague claimed.
The layout the algorithm generates condensed indented blocks. Within a
block, it inserts a newline when the distance to the next break point plus
the current position is greater than the space remaining on the current
line. Thus if S-Expression lists are rendered as blocks with indent two,
and every element in a list is separated by a break point of length one,
with the proper margin, you would see:
(one thing) (two thing)
(three thing) (four thing))
As an exercise, the book asks you to implement group indent, where if any
break point in a group inserts a newline, they all do. So with that layout,
one would get:
The C version I wrote supports this layout, but I didn't bother with that
extension for the Haskell version.
On the strictness annotations, my reasons for them are the usual ones,
primarily to prevent memory leaks due to dragging, but a performance boost
is always welcome. At some point, I plan to profile the code with and
without the annotations, and find out where they are needed.
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