[GHC] #960: Lexical call site string

[GHC]

#960: Lexical call site string
--------------------------------+-------------------------------------------
 Reporter:  paul at cogito.org.uk  |          Owner:         
     Type:  feature request     |         Status:  new    
 Priority:  normal              |      Milestone:         
Component:  Compiler            |        Version:  6.6    
 Severity:  normal              |     Resolution:         
 Keywords:                      |     Difficulty:  Unknown
 Testcase:                      |   Architecture:  Unknown
       Os:  Unknown             |  
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Comment (by simonpj):

 A neat way to do this might be to extend Template Haskell slightly, to
 provide
 {{{
   currentLocation :: Q (Filepath, Int)
 }}}
 giving the filename and location of the current splice.  (This is rather
 similar to the existing Template Haskell function
 [http://www.haskell.org/ghc/docs/latest/html/libraries/template-haskell
 /Language-Haskell-TH-Syntax.html#v%3AcurrentModule currentModule].)
 Then you could define
 {{{
   callSite :: ExpQ
   callSite = do { (f,n) <- currentLocation
                    ; return (LitE (StringL (f ++ ":" ++ show n))) }
 }}}
 And use it thus:
 {{{
   error ("woggle at" ++ $callSite)
 }}}
 Since the Template Haskell splice `$callSite` is a TH splice, it's ok for
 it to grab contextual information.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/960>
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