id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
4126	Order of members reversed when a template haskell instance declaration quotation is pretty-printed	lilac		"This broken file:

{{{
{-# LANGUAGE TemplateHaskell #-}                                                                                                                                                                                                             
(+1) [d| instance Monad ((,) a) where return = (,) undefined; (a,x) >>= f = f x |]
}}}

Gives the following error:

{{{
    No instance for (Num                                                                                                                                                                                                                     
                       (Language.Haskell.TH.Syntax.Q [Language.Haskell.TH.Syntax.Dec]))                                                                                                                                                      
      arising from the literal `1' at test.hs:2:2                                                                                                                                                                                            
    Possible fix:                                                                                                                                                                                                                            
      add an instance declaration for                                                                                                                                                                                                        
      (Num                                                                                                                                                                                                                                   
         (Language.Haskell.TH.Syntax.Q [Language.Haskell.TH.Syntax.Dec]))                                                                                                                                                                    
    In the second argument of `(+)', namely `1'                                                                                                                                                                                              
    In the expression:                                                                                                                                                                                                                       
        (+ 1)                                                                                                                                                                                                                                
          [d|                                                                                                                                                                                                                                
              instance Monad ((,) a) where                                                                                                                                                                                                   
                  { (a, x) >>= f = f x                                                                                                                                                                                                       
                    return = (,) undefined } |]
}}}

The error has reversed the order of members in the declaration. However, if I inspect the AST generated from the quotation, they are in the correct order. Hence I suspect the pretty-printer is reversing them."	bug	closed	normal	7.4.1	Template Haskell	6.12.2	fixed			Unknown/Multiple	Unknown/Multiple	None/Unknown