[Haskell-cafe] An Haskell implementation of a sweep line algorithm for the detection of segments intersection

[vince vegga]

Hi,

Here is my Haskell implementation of the Shamos and Hoey algorithm for
detecting segments intersection in the plane:

http://neonstorm242.blogspot.com/2010/12/sweep-line-algorithm-for-detection-of.html

I'm new to Haskell, so any useful comments will be appreciated.

- Eran

[Serguey Zefirov]

2010/12/6 vince vegga <megat...@gmail.com>:

> Here is my Haskell implementation of the Shamos and Hoey algorithm for
> detecting segments intersection in the plane:
>
> http://neonstorm242.blogspot.com/2010/12/sweep-line-algorithm-for-detection-of.html

Quite good, actually.

Myself, I rarely write code that is on par with yours. ;)

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[Henning Thielemann]

In sweepLine, things like

| a = False
| otherwise = x

can be written as (not a && x) and

if a then True else x

as (a || x).

In handleLeftEndpoint you can create (events,updateLine) outside the case
analysis, since this is common to all cases.

In general you can find hints in:
http://www.haskell.org/haskellwiki/Haskell_programming_tips
and in
http://www.haskell.org/haskellwiki/Category:Style

[smkh...@gmail.com]

Hi, I tried the above algorithm with some inputs such as [((1.25, 1), (2.85, 3.8)), ((4.5, 2.13), (1.75, 2.65)), ((1.5, 0.5), (3.5, 2.5))] but I get the following error: "Program error: Map.findIndex: element is not in the map"

May I know what the problem is? The algorithm seems to work for some other inputs though.