deriving Ix with custom ifThenElse causes "Bad call to tagToEnum#"
$ cat IfThenElseIx.hs
{-# LANGUAGE RebindableSyntax #-}
module IfThenElseIx where
import Data.Ix (Ix, )
import Prelude
ifThenElse :: Bool -> a -> a -> a
ifThenElse True x _ = x
ifThenElse False _ x = x
data T = A | B deriving (Eq, Ord, Ix)
$ ghci-8.0.0.20160109 IfThenElseIx.hs
GHCi, version 8.0.0.20160109: http://www.haskell.org/ghc/ :? for help
[1 of 1] Compiling IfThenElseIx ( IfThenElseIx.hs, interpreted )
IfThenElseIx.hs:13:35: error:
• Bad call to tagToEnum# at type a_a2ky
Specify the type by giving a type signature
e.g. (tagToEnum# x) :: Bool
• In the second argument of ‘ifThenElse’, namely
‘(GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#))’
In the expression:
if (GHC.Prim.tagToEnum# (c# GHC.Prim.>=# a#)) then
(GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#))
else
False
In a case alternative:
c#
-> if (GHC.Prim.tagToEnum# (c# GHC.Prim.>=# a#)) then
(GHC.Prim.tagToEnum# (c# GHC.Prim.<=# b#))
else
False
When typechecking the code for ‘GHC.Arr.inRange’
in a derived instance for ‘Ix T’:
To see the code I am typechecking, use -ddump-deriv
Failed, modules loaded: none.
Trac metadata
Trac field |
Value |
Version |
8.0.1-rc1 |
Type |
Bug |
TypeOfFailure |
OtherFailure |
Priority |
normal |
Resolution |
Unresolved |
Component |
Compiler |
Test case |
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Differential revisions |
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BlockedBy |
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Related |
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Blocking |
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CC |
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Operating system |
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