[Haskell-cafe] what does ' mean?

[Sun Yi Ming]

the xs' is just a variable as xs,xs_, _xs. perhaps imply some relations with the counterpart without apostrophe suffix,but this is not mandatory.
----- Original Message ----- 
From: "Logesh Pillay" <logesh at iafrica.com>
To: <haskell-cafe at haskell.org>
Sent: Monday, July 18, 2005 3:37 AM
Subject: [Haskell-cafe] what does ' mean?


> Dear list
> 
> A v. newbie question.
> 
> I found the following code on the web
> 
> /-- Andrew Bromage
> /
> /-- If you're doing permutations, then I suppose you want this too:
> //-- (subLists might be a more suggestive name)
> /combinations *:: [a] -> [[a]]
> *combinations [] = [[]]
> combinations (x:xs)
>    = combinations xs ++ [ x:xs' | xs' <- combinations xs ]
> 
> What does ' (apostrophe) mean?  I see no reference to it in Simon 
> Thompson's book.
> 
> Thanks
> 
> Logesh
> 
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