[Haskell-beginners] consing an element to a list inside a file

[Brent Yorgey]

On Wed, Feb 10, 2010 at 09:52:48PM +0100, kane96 at gmx.de wrote:
> Hi,
> I want to add an element to a list inside a haskell file:
> mylist = [1,2,3,4]
> 0:mylist
> in Prelude it works fine, but when I do it in a file I get the error: 
> parse error (possibly incorrect indentation)
> Failed, modules loaded: none.
> in a line after this two that doesn't exist

A Haskell file is simply a list of declarations, i.e. definitions of
data types, classes, and functions.  You cannot just have an
expression by itself in a Haskell file.  You can write expressions at
a ghci prompt (which I assume is what you meant) because that is what
ghci is for: evaluating expressions.

Why do you want 0:mylist by itself in a Haskell file?  What is its
purpose?  Note that it will not modify the value of mylist (indeed,
you *cannot* modify the value of mylist once it has been defined).

-Brent