Is there an unsigned integer type that will warn about negative literals?

Question

Recent versions of ghc will warn you if an integer literal is outside a given type's range. For example:

$ ghci >>> let x = 330492039485 :: Data.Word.Word8 <interactive>:2:9: Warning:     Literal 330492039485 is out of the GHC.Word.Word8 range 0..255 

However, ghc will not warn about negative numeric literals for Data.Word types. Instead, it underflows (intentionally, according to the documentation):

>>> let x = -1 :: Data.Word.Word8 >>> x 255 

Are there any types that will warn about negative literals or is there a way I can create my own custom type that does warn?

Answer 1

By default, a literal like -1 is desugared to negate (fromInteger 1). There is however a language extension NegativeLiterals that causes it to desugar as fromInteger (-1) instead. If you enable that you do get a warning:

Prelude> :m +Data.Word Prelude Data.Word> :set -W Prelude Data.Word> :set -XNegativeLiterals Prelude Data.Word> -1 :: Word  <interactive>:74:1: Warning:     Literal -1 is out of the Word range 0..18446744073709551615 18446744073709551615 Prelude Data.Word> 

Alternatively, you could make your own type that redefined negate, but then you would presumably only get a runtime error.