Template haskell rejects duplicate instances before they're spliced
Suppose I want to see (from within ghci) how to write an instance declaration in the TH AST. I try:
```
Prelude> runQ $ [d| instance Monad Maybe where |]
<interactive>:1:13:
Duplicate instance declarations:
instance Monad Maybe -- Defined at <interactive>:1:13-23
instance Monad Maybe -- Defined in Data.Maybe
In the Template Haskell quotation
[d|
instance Monad Maybe where |]
In the expression:
[d|
instance Monad Maybe where |]
In the definition of `it':
it = [d|
instance Monad Maybe where |]
```
This seems ridiculous; I'm not trying to create an instance, just to create a TH AST fragment.
<details><summary>Trac metadata</summary>
| Trac field | Value |
| ---------------------- | ---------------- |
| Version | 6.12.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Template Haskell |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture | |
</details>
<!-- {"blocked_by":[],"summary":"Template haskell rejects duplicate instances before they're spliced","status":"New","operating_system":"","component":"Template Haskell","related":[],"milestone":"","resolution":"Unresolved","owner":{"tag":"Unowned"},"version":"6.12.1","keywords":[],"differentials":[],"test_case":"","architecture":"","cc":[""],"type":"Bug","description":"Suppose I want to see (from within ghci) how to write an instance declaration in the TH AST. I try:\r\n\r\n{{{\r\nPrelude> runQ $ [d| instance Monad Maybe where |] \r\n \r\n<interactive>:1:13: \r\n Duplicate instance declarations: \r\n instance Monad Maybe -- Defined at <interactive>:1:13-23 \r\n instance Monad Maybe -- Defined in Data.Maybe \r\n In the Template Haskell quotation \r\n [d| \r\n instance Monad Maybe where |] \r\n In the expression: \r\n [d| \r\n instance Monad Maybe where |] \r\n In the definition of `it': \r\n it = [d| \r\n instance Monad Maybe where |]\r\n}}}\r\n\r\nThis seems ridiculous; I'm not trying to create an instance, just to create a TH AST fragment.","type_of_failure":"OtherFailure","blocking":[]} -->
issue