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  • #15362

Closed
Open
Opened Jul 11, 2018 by Richard Eisenberg@raeDeveloper

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
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture
Assignee
Assign to
8.8.1
Milestone
8.8.1 (Past due)
Assign milestone
Time tracking
None
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Reference: ghc/ghc#15362