#3108: Do a better job of solving recursive type-class constraints with
functional
dependencies
----------------------------------------+-----------------------------------
Reporter: simonpj | Owner:
Type: bug | Status: new
Priority: high | Milestone: 7.6.1
Component: Compiler (Type checker) | Version: 6.10.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
----------------------------------------+-----------------------------------
Changes (by simonpj):
* cc: dimitris@… (added)
* failure: => None/Unknown
* priority: lowest => high
Comment:
With the new constraint solver we an ASSERT error for this program:
{{{
{-# LANGUAGE OverlappingInstances, UndecidableInstances,
MultiParamTypeClasses,
FunctionalDependencies, FlexibleInstances #-}
module T3108 where
-- Direct recursion terminates (typechecking-wise)
class C0 x
where
m0 :: x -> ()
m0 = const undefined
instance (C0 x, C0 y) => C0 (x,y)
instance C0 Bool
instance C0 (x,Bool) => C0 x
foo :: ()
foo = m0 (1::Int)
-- Indirect recursion does not terminate (typechecking-wise)
class C1 x
where
m1 :: x -> ()
m1 = const undefined
instance (C1 x, C1 y) => C1 (x,y)
instance C1 Bool
instance (C2 x y, C1 (y,Bool)) => C1 x
class C2 x y | x -> y
instance C2 Int Int
-- It is this declaration that causes nontermination of typechecking.
bar :: ()
bar = m1 (1::Int)
}}}
Thus:
{{{
simonpj@cam-05-unx:~/tmp$ ~/5builds/HEAD/inplace/bin/ghc-stage1 -c
T3108.hs -dcore-lint -fforce-recomp
setEvBind
Cycle in evidence binds, evvar = $dC1{v aep} [lid]
{$dC1{v adw} [lid]
= main:T3108.$fC1x{v r1} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
y{tv aej} [tcs]]
[$dC2{v aek} [lid],
$dC1{v ael} [lid]],
$dC2{v aek} [lid]
= $dC2{v aeo} [lid] `cast` (main:T3108.C2{tc r7}
<ghc-prim:GHC.Types.Int{(w) tc 3J}>
(Sym cobox{v aen} [lid])),
$dC1{v ael} [lid]
= $dC1{v aep} [lid] `cast` (main:T3108.C1{tc r9}
(Sym cobox{v aen} [lid],
<ghc-prim:GHC.Types.Bool{(w) tc
3c}>)),
cobox{v aen} [lid] = CO <ghc-prim:GHC.Types.Int{(w) tc 3J}>,
$dC2{v aeo} [lid]
= main:T3108.$fC2IntInt{v r0} [lidx[DFunId]] @[] [],
$dC1{v aep} [lid]
= main:T3108.$fC1(,){v r3} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC1{v adw} [lid],
$dC1{v aeq} [lid]]}
setEvBind
Cycle in evidence binds, evvar = $dC0{v aer} [lid]
{$dC1{v adw} [lid]
= main:T3108.$fC1x{v r1} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
y{tv aej} [tcs]]
[$dC2{v aek} [lid],
$dC1{v ael} [lid]],
$dC0{v ady} [lid]
= main:T3108.$fC0x{v r4} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J}]
[$dC0{v aer} [lid]],
$dC2{v aek} [lid]
= $dC2{v aeo} [lid] `cast` (main:T3108.C2{tc r7}
<ghc-prim:GHC.Types.Int{(w) tc 3J}>
(Sym cobox{v aen} [lid])),
$dC1{v ael} [lid]
= $dC1{v aep} [lid] `cast` (main:T3108.C1{tc r9}
(Sym cobox{v aen} [lid],
<ghc-prim:GHC.Types.Bool{(w) tc
3c}>)),
cobox{v aen} [lid] = CO <ghc-prim:GHC.Types.Int{(w) tc 3J}>,
$dC2{v aeo} [lid]
= main:T3108.$fC2IntInt{v r0} [lidx[DFunId]] @[] [],
$dC1{v aep} [lid]
= main:T3108.$fC1(,){v r3} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC1{v adw} [lid],
$dC1{v aeq} [lid]],
$dC1{v aeq} [lid]
= main:T3108.$fC1Bool{v r2} [lidx[DFunId(nt)]] @[] [],
$dC0{v aer} [lid]
= main:T3108.$fC0(,){v r6} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC0{v ady} [lid],
$dC0{v aes} [lid]]}
simonpj@cam-05-unx:~/tmp$ ~/5builds/HEAD/inplace/bin/ghc-stage1 -c
T3108.hs -dcore-lint -fforce-recomp
setEvBind
Cycle in evidence binds, evvar = $dC1{v aep} [lid]
{$dC1{v adw} [lid]
= main:T3108.$fC1x{v r1} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
y{tv aej} [tcs]]
[$dC2{v aek} [lid],
$dC1{v ael} [lid]],
$dC2{v aek} [lid]
= $dC2{v aeo} [lid] `cast` (main:T3108.C2{tc r7}
<ghc-prim:GHC.Types.Int{(w) tc 3J}>
(Sym cobox{v aen} [lid])),
$dC1{v ael} [lid]
= $dC1{v aep} [lid] `cast` (main:T3108.C1{tc r9}
(Sym cobox{v aen} [lid],
<ghc-prim:GHC.Types.Bool{(w) tc
3c}>)),
cobox{v aen} [lid] = CO <ghc-prim:GHC.Types.Int{(w) tc 3J}>,
$dC2{v aeo} [lid]
= main:T3108.$fC2IntInt{v r0} [lidx[DFunId]] @[] [],
$dC1{v aep} [lid]
= main:T3108.$fC1(,){v r3} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC1{v adw} [lid],
$dC1{v aeq} [lid]]}
setEvBind
Cycle in evidence binds, evvar = $dC0{v aer} [lid]
{$dC1{v adw} [lid]
= main:T3108.$fC1x{v r1} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
y{tv aej} [tcs]]
[$dC2{v aek} [lid],
$dC1{v ael} [lid]],
$dC0{v ady} [lid]
= main:T3108.$fC0x{v r4} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J}]
[$dC0{v aer} [lid]],
$dC2{v aek} [lid]
= $dC2{v aeo} [lid] `cast` (main:T3108.C2{tc r7}
<ghc-prim:GHC.Types.Int{(w) tc 3J}>
(Sym cobox{v aen} [lid])),
$dC1{v ael} [lid]
= $dC1{v aep} [lid] `cast` (main:T3108.C1{tc r9}
(Sym cobox{v aen} [lid],
<ghc-prim:GHC.Types.Bool{(w) tc
3c}>)),
cobox{v aen} [lid] = CO <ghc-prim:GHC.Types.Int{(w) tc 3J}>,
$dC2{v aeo} [lid]
= main:T3108.$fC2IntInt{v r0} [lidx[DFunId]] @[] [],
$dC1{v aep} [lid]
= main:T3108.$fC1(,){v r3} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC1{v adw} [lid],
$dC1{v aeq} [lid]],
$dC1{v aeq} [lid]
= main:T3108.$fC1Bool{v r2} [lidx[DFunId(nt)]] @[] [],
$dC0{v aer} [lid]
= main:T3108.$fC0(,){v r6} [lidx[DFunId(nt)]] @[ghc-
prim:GHC.Types.Int{(w) tc 3J},
ghc-
prim:GHC.Types.Bool{(w) tc 3c}]
[$dC0{v ady} [lid],
$dC0{v aes} [lid]]}
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3108#comment:7>
GHC <http://www.haskell.org/ghc/>
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