[Haskell-beginners] The (x:xs) in function parameter is a tuple?

[Graham Gill]

Hi Nan, are you just confused about the use of the parentheses "(" and ")"?

(x1,x2), (x1,x2,x3), ... are tuples in Haskell, but (x:xs) is not. 
(There's no "one-ple", or 1-tuple, in Haskell.) In

occurs value [] = 0
occurs value (x:xs) = (if value == x then 1 else 0) + occurs value xs

the "(" and ")" around "x:xs" are just there for grouping, for operator 
precedence reasons. Function application binds more tightly than ":". If 
you leave the parentheses off, such as in

occurs value x:xs = ...

you'll get a parse error.

Graham


On 2/24/2016 5:31 AM, Nan Xiao wrote:
> Hi all,
>
> Greetings from me!
>
> I am confused about the function parameters and tuple. E.g.:
>
> occurs value [] = 0
> occurs value (x:xs) = (if value == x then 1 else 0) + occurs value xs
>
> should we consider (x:xs) as a tuple?
>
> Thanks in advance!
>
> Best Regards
> Nan Xiao
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