Context reduction stack overflow can take very long
The following code, taken from the "Haskell Type Constraints Unleashed" paper:
{-# LANGUAGE TypeFamilies #-}
type family TF a :: *
type instance TF (a,b) = (TF a, TF b)
t :: (a ~ TF (a,Int)) => Int
t = undefined
fails almost immediately with Context reduction stack overflow
on GHC 7.2, but seems to loop forever with 7.4.1-rc2. Setting -fcontext-stack
to 20
results in near immediate termination with the same error. But #5395 (closed) raised the context stack size default to 200
, which makes this code (that does not use -XUndecidableInstances
) take "forever" to compile.
Trac metadata
Trac field | Value |
---|---|
Version | 7.4.1-rc2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler (Type checker) |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |