[Haskell-beginners] safetail problem

[Tom Murphy]

If:
x = [1,2,3] :: [Int]
y = [0] :: [Int]
z = 0

then:
[y,x] == [[0],[1,2,3]] :: [[Int]]
    - a list of lists. It doesn't get simplified into [0,1,2,3].

(z,x) == (0,[1,2,3]) :: (Int, [Int])
    - a tuple, whose first element is an Int, and whose second element
is a list of Ints ([Int])

z:x == [0,1,2,3] :: [Int]


The third one is what you're looking for. It's called "cons."

Tom


On 7/12/11, Roelof Wobben <rwobben at hotmail.com> wrote:
>
>
> Hello,
>
>
>
> I use Programming in Haskell from Graham Hutton.
>
>
>
> But I can't find anything in the first 4 chapters from that book why I must
> use (0,x) en what that means.
>
>
>
> Roelof
>
>
>
>
>
>
> ----------------------------------------
>> Date: Tue, 12 Jul 2011 15:21:46 -0400
>> Subject: Re: [Haskell-beginners] safetail problem
>> From: amindfv at gmail.com
>> To: rwobben at hotmail.com
>> CC: beginners at haskell.org
>>
>> _ isn't a value: it's a wildcard character for pattern matching.
>>
>> Also, if x = [1,2,3], [0,x] is the wrong way to make a list. The right
>> way is (0:x) (":" is "cons")
>>
>> What resource are you learning from?
>>
>> On 7/12/11, Roelof Wobben <rwobben at hotmail.com> wrote:
>> >
>> >
>> > Hello,
>> >
>> >
>> >
>> > As a exercise I need to rewrite the tail function into a safetail
>> > function
>> > by using conditions.
>> >
>> >
>> >
>> > So I made this : http://codepad.org/bKcCUdqy
>> >
>> >
>> >
>> > But as you can see there is a error message.
>> >
>> >
>> >
>> > Can anyone explain me how to solve this ?
>> >
>> >
>> >
>> > Roelof
>> >
>> >
>> >
>> >
>> >
>> >
>> > _______________________________________________
>> > Beginners mailing list
>> > Beginners at haskell.org
>> > http://www.haskell.org/mailman/listinfo/beginners
>> > 		 	   		
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