[ ghc-Bugs-1162762 ] fromInteger-related pattern match overlap warnings

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Bugs item #1162762, was opened at 2005-03-13 20:19
Message generated for change (Comment added) made by nobody
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Category: Compiler
Group: 6.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Ashley Yakeley (ashley-y)
Assigned to: Simon Peyton Jones (simonpj)
Summary: fromInteger-related pattern match overlap warnings

Initial Comment:
The compiler incorrectly gives "Warning: Pattern match(es) are 
overlapped" for this file:

{-# OPTIONS -Werror #-}

module Buggy where

	instance (Num a) => Num (Maybe a) where
		(Just a) + (Just b) = Just (a + b)
		_ + _ = Nothing
		(Just a) - (Just b) = Just (a - b)
		_ - _ = Nothing
		(Just a) * (Just b) = Just (a * b)
		_ * _ = Nothing
		negate (Just a) = Just (negate a)
		negate _ = Nothing
		abs (Just a) = Just (abs a)
		abs _ = Nothing
		signum (Just a) = Just (signum a)
		signum _ = Nothing
		fromInteger = Just . fromInteger

	f :: Maybe Int -> Int
	f 1 = 1
	f Nothing = 2
	f _ = 3


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Comment By: Nobody/Anonymous (nobody)
Date: 2005-11-29 20:15

Message:
Logged In: NO 

If we define the first line as:

f (Just 1) = 1

there is no problem. 

----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=108032&aid=1162762&group_id=8032