[Haskell-beginners] Finding Keith Numbers with Haskell

[Alexander Berntsen]

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On 11/11/14 16:17, Kim-Ee Yeoh wrote:
> On Tue, Nov 11, 2014 at 8:26 PM, Jack Mott <jack.mott at gmail.com> 
> wrote:
> 
>> Thanks, is the notation with the single quote (isKeith') a 
>> convention for helper functions or does it actually change 
>> something about the program?
> 
> 
> An unspoken coding convention.
> 
> Function foo' would be read "foo-prime". E.g.of usage:
> haskell-prime is the next standard of haskell, which became moot
> because you need good vibes for diverse peoples to collaborate on
> such an undertaking, including supporting it by writing more than
> one implementation.
> 
> Strictly syntax, the compiler doesn't treat it differently from
> any other name label.
> 
> So yes, you could have foo-double-prime and so forth.
It's inherited from maths (like everything else). Very commonly used
for a changed/new version of something. Comes up a lot in games
programming. One banal example:

update :: World -> World
update (World p p2 b e) =
  let p'  = update p
      p2' = update p2
      b'  = update b
      e'  = update e
  in  World p' p2' b' e'
  where update = draw . move . react
- -- 
Alexander
alexander at plaimi.net
https://secure.plaimi.net/~alexander
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