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

mysecondlist = 0:mylist that's was I was searching for, but how can I add the element to the same list? I have to get any number of inputs from the user and at the end, if he doesn't want to make more inputs, I have to print a list with all the inputs he did. -------- Original-Nachricht --------

Datum: Wed, 10 Feb 2010 22:21:13 +0100 Von: Daniel Fischer An: beginners@haskell.org CC: kane96@gmx.de Betreff: Re: [Haskell-beginners] consing an element to a list inside a file

Am Mittwoch 10 Februar 2010 21:52:48 schrieb kane96@gmx.de:

...

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

0:mylist

is a plain value. At the ghci or hugs prompt, if you enter an expression (4, 3*7+5, [0 .. 10],...), that means "evaluate the expression and print the result" (unless it's a value of type IO a, then it means "execute this action"). In a source file, you write definitions,

name = expression to be bound to name

func arg1 arg2 = body

etc.

You can have pattern bindings in a source file,

(a,b) = ([0 .. 100],True)

-- defines a and b

0:mylist = map (`mod` 7) [14 .. 100]

-- defines mylist as [1,2,3,4,5,6,0,1,...,1,2]

0:myotherlist = [4,5,6]

{- will fail with ghci> myotherlist *** Exception: PatTest.hs:4:0-22: Irrefutable pattern failed for pattern 0 : myotherlist

when demanded -} , so that's what the parser expected, a '=' and an expression which defines mylist. Since it didn't find a '=' on the same line, it tried the next (where it found end of file, another definition or whatever) where it reported the parse error.

Probably you wanted

mysecondlist = 0:mylist

?

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