Why give me error? [closed]

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The cause for the error you’re getting here is the use of the name count&remove: identifiers in Haskell have to be either alphanumeric (e.g. count_and_remove) or symbolic (e.g. ==, ++, etc.). Identifiers can’t contain both alphanumeric characters and symbols.

But that’s just one problem. You also have a reference to y on line 9 that doesn’t refer to anything. And you seem not to quite understand yet how pattern matching works in function definitions. For example, your first function could be defined just as:

first (x:xs) = x

This isn’t great in itself, both because there’s a standard Prelude function called head that does this, and because it’s what’s called a partial function (https://wiki.haskell.org/Partial_functions).

The same sort of comment applies to your count&remove function, which you could write as:

count_and_remove xs = length xs - length (remove1 xs)

(No need to pattern match with (x:xs) here.)

If you are looking for more learning resources, a popular tutorial is Learn You A Haskell. You can also ask for help on the haskell-beginners mailing list or have a conversation in the #haskell channel on irc.freenode.net.

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