[Haskell-cafe] writer monad help

[iskaldur]

I'm trying to learn to use the Writer Monad, but I'm having trouble with the
following very simple program:

import Control.Monad.Writer
foo :: Writer String Int
foo = tell "hello"

Basically, I was trying to figure out the 'tell' function, so I want foo to
return ((), "hello").

But I get this error:
Couldn't match `Int' against `()'
      Expected type: Writer String Int
      Inferred type: Writer String ()
    In the application `tell "hello"'
    In the definition of `foo': foo = tell "hello"

What am I supposed to do? Write my own version of tell for Writer String
Int? How exactly do I do this?
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