Summarizing the comments, and possible problems and solutions: There are no errors in your code, you can even try it online here; If you are using a text editor, check if you save your changes. I'm a bit new to Haskell but I've been working this problem for a couple hours with no luck. First, there is Variable not in scope: ghci :: t0 -> b0 -> c Variable not in scope : file Variable not in scope : hs :: a -> b0 とエラーが出て先に進めません。 ネットで検索してみましたが、わかりません。 どうか助言をお願 … I'm trying to implement something similar to a filter, except a predicate and list is passed to a function and it returns a tuple of two lists, one which is filtered by the predicate and one which is not. 'Variable not in scope" when using GHCi with `-fobject-code` Since b98ff3cc was landed ( #7253 (closed) ), you don't need let to define stuff in GHCi: $ ghci Prelude> x = 3 Prelude> x 3 Often there is a solution that is Haskell 98. Although Scoped Type Variables are often a simple solution, they are not available in all compilers.