#1982: Spurious "defined but not used" warnings for constructors of types
deriving
Read
-------------------------+--------------------------------------------------
Reporter: Eelis- | Owner:
Type: bug | Status: new
Priority: low | Milestone:
Component: Compiler | Version: 6.8.2
Severity: minor | Keywords:
Difficulty: Unknown | Testcase:
Architecture: Unknown | Os: Unknown
-------------------------+--------------------------------------------------
Consider the following code:
{{{
data D = D { ds :: String, db :: Bool }
deriving (Read, Show)
main :: IO ()
main = do
let s = "D { ds = \"oi\", db = True }"
print (ds (read s))
print (db (read s))
}}}
With -Wall, ghc emits the following warning:
{{{
Warning: Defined but not used: data constructor `D'
}}}
I think this warning is not justified, because the D constructor ''is''
used to parse s.
The testcase above was derived from a program where D held a bunch of
configuration fields for the program, and s was read from configuration
file.
I would think the fix should be a rule along the lines of: if a data type
derives from Read, then all of its constructors and field names are
considered used.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1982>
GHC <http://www.haskell.org/ghc/>
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