deriving Read leads to "no parse"
The program
------ Start Offending Program -----
module Main
where
data T = C (Maybe Int) Int
deriving (Show, Read, Eq)
main =
do
let v = C Nothing 1
print v
print $ read (show v) == v
------ End Offending Program -----
leads to
AttitudeAdjuster chak 5 (~/haskell): ghc Main.hs
AttitudeAdjuster chak 6 (~/haskell): ./a.out
C Nothing 1
Fail: Prelude.read: no parse
AttitudeAdjuster chak 7 (~/haskell):
Experimentation suggests that it is the `Maybe' type
appearing in the type for which Read is derived that
causes the problem. This problem does *not* occur with
GHC 5.04; ie, has been introduced with patchlevel 1.
(I am not sure whether it is a problem in the Prelude
or the deriving mechanism.)
This bug is pretty serious for me, as it utterly breaks
C->Haskell.
/me waits for GHC 5.04.2...
Trac metadata
Trac field |
Value |
Version |
5.04.1 |
Type |
Bug |
TypeOfFailure |
OtherFailure |
Priority |
high |
Resolution |
ResolvedFixed |
Component |
Compiler |
Test case |
|
Differential revisions |
|
BlockedBy |
|
Related |
|
Blocking |
|
CC |
|
Operating system |
|
Architecture |
|