What does :: (double colon) stand for in Haskell?

Question

I see and use the :: symbols everywhere but still don\'t know what the :: symbol means when programming in Haskell, e.g.

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Answer 1

When you have a big scary-looking typechecking error, you can (temporarily) wrap parts of your code in (myexpression :: MyType) to explicitly state to the compiler which type you're expecting myexpression to have. This will often help the compiler give you better error messages.