Need help groking the statement: expression1 in term:expression2

[Olumide]

Hello List,

I'd appreciate help understanding the second line of following block of
code (from LYH, first line added for completeness),

http://learnyouahaskell.com/input-and-output#randomness
randoms' :: (RandomGen g, Random a) => g -> [a]
randoms' gen = let (value, newGen) = random gen in value:randoms' newGen

The part I'm really struggling with is random gen in value:randoms' newGen

Thanks,

- Olumide
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[Quanyang Liu]

On Tue, Mar 22 2016 at 18:43:46 +0800, Olumide wrote:
> Hello List,
>
> I'd appreciate help understanding the second line of following block
> of code (from LYH, first line added for completeness),
>
> http://learnyouahaskell.com/input-and-output#randomness
> randoms' :: (RandomGen g, Random a) => g -> [a]
> randoms' gen = let (value, newGen) = random gen in value:randoms' newGen
>

It's equivalent to the following:
     randoms' gen = let (value, newGen) = random gen
                    in value:(randoms' newGen)

> The part I'm really struggling with is random gen in value:randoms' newGen
>
> Thanks,
>
> - Olumide

--
Thanks,
Quanyang
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[Sumit Sahrawat, Maths & Computing, IIT (BHU)]

On 22-Mar-2016 4:14 pm, "Olumide" <[hidden email]> wrote:
> randoms' :: (RandomGen g, Random a) => g -> [a]
> randoms' gen = let (value, newGen) = random gen in value:randoms' newGen

"random gen" returns a pair, whose first element is a random value, and the second element is a new generator.

The cons (:) operator takes two values, one is an element, and the other is a list. It returns a new list with the provided arguments as head and tail.

Ultimately, randoms' gen returns a list whose first element is a random value, and the rest of the list is the result of calling randoms' on the newly produced generator. Recursively, it generates an infinite lazy list of random elements.

Hope this helps :)

Regards,
  Sumit

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