Re: [GHC] #10824: Strict let-bindings are processed backwards (was: Let-bindings of kind # are processed backwards)

4 Sep 2015

      #10824: Strict let-bindings are processed backwards
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        Reporter:  ezyang            |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  normal            |               Milestone:
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
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Description changed by ezyang:

Old description:
...
Consider this module:
{{{
{-# LANGUAGE MagicHash #-}
import GHC.Exts
main = do let x = error "bar" :: Int#
              y = error "foo" :: Int#
          print (I# x + I# y)
}}}
When you run this, you will get the error "foo" and not the error "bar".
This is backwards!
New description:

 Consider this module:

 {{{
 main = do let !x = error "bar"
               !y = error "foo"
           print (x + y)
 }}}
 or this analogous module:

 {{{
 {-# LANGUAGE MagicHash #-}
 import GHC.Exts
 main = do let x = error "bar" :: Int#
               y = error "foo" :: Int#
           print (I# x + I# y)
 }}}

 When you run these, you will get the error "foo" and not the error "bar".
 This is backwards!

--

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Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10824#comment:1
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