Template Haskell ignores bad type family definitions
This garbage is accepted:
data Nat = Zero | Succ Nat
$( [d| type family a + b where
Maybe Zero b = b
Succ a + b = Succ (a + b) |] )Note the Maybe photo-bombing in the first equation. The problem is that TH uses the symbol declared in the family head for all the equations, ignoring what's actually there. This is sad.
Trac metadata
| Trac field | Value |
|---|---|
| Version | 8.4.3 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
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| Blocking | |
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| Operating system | |
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