Nested Let syntax in haskell confusion

Question

main = let sumSquares = sum (map (^2) [1..100]) 
           squaredSum = sum [1..100] ^ 2 
           in sumSquares - squaredSum

New to Haskell, so I've been going back through Project Euler. I know my solution is sound, and it works when I don't bother with any lets.

For some reason, this gives me an error message. Can you help? Thank you!

Answer 1

You have chosen to name this term main , without giving it the correct type. A Haskell module with a main term is expected to define it with type IO () , but you have given it an expression that looks something like Num a => a , by virtue of the - This error happens because Haskell is looking for some sort of way to make IO .. an instance of Num , which it isn't.

Try naming it something else.