Hi all, I've been going over my code trying to get it all to compile with "ghc -Wall -Werror", without introducing constructs that would make my code the laughing stock of the dynamic typing community. They already think we're nuts; my daydreams are of a more computer literate society where Jessie Helms stands up in the U.S. Senate to read aloud my type declarations to the derisive laughter of the Ruby and Lisp parties. There's a fine line between my opinion as to how GHC should issue warnings, and a legitimate bug report. I've already submitted a bug report for the need to declare the type of the wildcard pattern, because I believe that the case is clear. Here, I'm seeking guidance. Perhaps I just don't know the most elegant construct to use? My sample code is this:
{-# OPTIONS_GHC -Wall -Werror #-}
module Main where
import Prelude hiding ((^)) import qualified Prelude ((^))
default (Int)
infixr 8 ^ (^) :: Num a => a -> Int -> a x ^ n = x Prelude.^ n
main :: IO () main = let r = pi :: Double x = r ^ (3 :: Int) y = r ^ 3 z = r Prelude.^ 3 in putStrLn $ show (x,y,z)
GHC issues a "Warning: Defaulting the following constraint(s) to type `Int'" for the definition of z. The definition of y glides through, so a qualified import and redefinition of each ambiguous operator does provide a work-around, but the code is lame. (I could always encapsulate it in a module Qualude.) If I import a module that I don't use, then "ghc -Wall -Werror" rightly complains. By analogy, if I use "default (Int)" to ask GHC to default to Int but the situation never arises, then GHC should rightly complain. Instead, if I use "default (Int)", GHC complains about defaulting anyways. In my opinion, this is a bug, but I'd like guidance before reporting it. Is there a more elegant way to handle the numeric type classes with "ghc -Wall -Werror" ? No one is forced to use "ghc -Wall -Werror", but it should be a practical choice. I've enjoyed the recent typing discussions here. On one hand, there's little difference between using dynamic typing, and writing incomplete patterns in a strongly typed language. On the other hand, how is an incomplete pattern any different from code that potentially divides by zero? One quickly gets into decidability issues, dependent types, Turing-complete type systems. My personal compromise is to use "ghc -Wall -Werror", live with the consequences, and get back to work. Perhaps I'll get over it, but that's a slippery slope back to Lisp.