GHC issueshttps://gitlab.haskell.org/ghc/ghc/-/issues2019-07-07T18:34:28Zhttps://gitlab.haskell.org/ghc/ghc/-/issues/10713Type family not reducing over data family2019-07-07T18:34:28ZacowleyType family not reducing over data familyGiven this code,
```
type family TEq t s where
TEq t t = 'True
TEq t s = 'False
data family T a
```
I expected this GHCi interaction to reduce:
`:kind! TEq (T Int) (T Bool)`
But it does not. It does reduce (to `'True`) if you inst...Given this code,
```
type family TEq t s where
TEq t t = 'True
TEq t s = 'False
data family T a
```
I expected this GHCi interaction to reduce:
`:kind! TEq (T Int) (T Bool)`
But it does not. It does reduce (to `'True`) if you instead ask,
`:kind! TEq (T Int) (T Int)`
Tested on GHC 7.10.2
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ----------------------- |
| Version | 7.10.2 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler (Type checker) |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"Type family not reducing over data family","status":"New","operating_system":"","component":"Compiler (Type checker)","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"7.10.2","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"Given this code,\r\n\r\n{{{\r\ntype family TEq t s where\r\n TEq t t = 'True\r\n TEq t s = 'False\r\ndata family T a\r\n}}}\r\n\r\nI expected this GHCi interaction to reduce:\r\n`:kind! TEq (T Int) (T Bool)`\r\n\r\nBut it does not. It does reduce (to `'True`) if you instead ask,\r\n\r\n`:kind! TEq (T Int) (T Int)`\r\n\r\nTested on GHC 7.10.2\r\n","type_of_failure":"OtherFailure","blocking":[]} -->7.10.3Richard Eisenbergrae@richarde.devRichard Eisenbergrae@richarde.dev