[Haskell-beginners] Concatenating lists

[Felipe Almeida Lessa]

On Thu, Mar 22, 2012 at 11:44 AM, Jan Erik Moström <lists at mostrom.pp.se> wrote:
> Hi,
>
> I've just started to learn Haskell and played around a bit and tried this
>
> 1: let x = [1,2,3]
> 2: let x = x ++ [4,5,6]
> 3: x
>
> The last line doesn't give a result. I assume that this is because 'x' is a name of a value, in the second line I redefine 'x' to a new value but Haskell doesn't evaluate the value until the last line but then 'x' becomes recursively defined in itself (the second x on line 2 is interpreted to refer to the value of the first x on line 2 and  not the value defined in line 1). This behavior is caused by the lazy evaluation in Haskell.
>
> Have I understood this correctly?

Your conclusion is correct, but your reasoning is not.  It's not due
to lazyness that x is recursively defined, it's because of the scope.
When you type your second x on the second line, that x will refer to
the closest (in scope) definition of something called x -- which is
the the definition of x on the second line itself.

Cheers,

-- 
Felipe.