Bugs item #1075259, was opened at 2004-11-29 14:00
Message generated for change (Settings changed) made by simonmar
You can respond by visiting:
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Category: Compiler (Parser)
Group: 6.2.2
Status: Open
Resolution: None
>Priority: 2
Submitted By: Nobody/Anonymous (nobody)
Assigned to: Nobody/Anonymous (nobody)
Summary: Wrong overlapped/missing pattern warnings
Initial Comment:
compiling:
module Overlap where
f (n+1) = 2
f 0 = 1
emits wrongly:
Warning: Pattern match(es) are overlapped
In the definition of `f': f 0 = ...
The Patterns are disjoint, aren't they? At least "f 0"
yields "1" when evaluated and negative inputs for f are
rejected. However the warning is not emitted if the two
equations are given in reversed order.
Christian ([EMAIL PROTECTED])
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Comment By: Simon Peyton Jones (simonpj)
Date: 2004-12-13 09:49
Message:
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user_id=50165
Here's another example, from Peter White
When I compile the following module with the -Wall option on
ghc v6.2.1
I get warnings:
Warning: Pattern match(es) are non-exhaustive
In a record-update construct: Patterns not matched D2.
The warnings occur at both of the indicated places in the
module.
Since the functions both handle all the cases of the data
type D, it
seems the warning should not be given.
data D = D1 { f1 :: Int } | D2
-- Use pattern matching in the argument
f :: D -> D
f d1@(D1 {f1 = n}) = d1 { f1 = f1 d1 + 1 } -- Warning here
f d = d
-- Use case pattern matching
g :: D -> D
g d1 = case d1 of
D1 { f1 = n } -> d1 { f1 = n + 1 } -- Warning here
also
D2 -> d1
----------------------------------------------------------------------
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