id,summary,reporter,owner,description,type,status,priority,milestone,component,version,resolution,keywords,cc,os,architecture,failure,difficulty,testcase,blockedby,blocking,related
4125,Template haskell rejects duplicate instances before they're spliced,lilac,,"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.",bug,closed,normal,7.4.1,Template Haskell,6.12.1,invalid,,,Unknown/Multiple,Unknown/Multiple,GHC rejects valid program,,,4230,,