[GHC] #9180: New magic function `staticError`

[GHC]

#9180: New magic function `staticError`
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       Reporter:  nomeata           |             Owner:  nomeata
           Type:  feature request   |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.8.2
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 While playing games with `RULES`, I had the need for a way to tell the
 compiler “please spit out an error message”, in my case if list fusion
 fails where the user explicitly requested for it.

 Currently I put an `error "List did not fuse"` in the code using a `RULE`,
 but what I’d really like to do is to put in a `staticError "List did not
 fuse"` that, if appearing in Core (say, after the final simplification)
 causes GHC to abort and print this message.

 (I’m tempted to use type level strings somehow to make sure that the
 parameter to `staticError` is not present at the value level, and also
 that the string is easier to obtain. I’ll see.)

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9180>
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