Mon Apr 20 07:25:25 PDT 2009 Simon Marlow <[email protected]>
* FIX #2845: Allow breakpoints on expressions with unlifted type
Ignore-this: 8d1b2624a4635b421032463219af604e
It turns out we can easily support breakpoints on expressions with
unlifted types, by translating
case tick# of _ -> e
into
let f = \s . case tick# of _ -> e
in f realWorld#
instead of just a plain let-binding. This is the same trick that GHC
uses for abstracting join points of unlifted type.
In #2845, GHC has eta-expanded the tick expression, changing the
result type from IO a to (# State#, a #), which was the reason the
tick was suddenly being ignored. By supporting ticks on unlifted
expressions we can make it work again, although some confusion might
arise because _result will no longer be available (it now has
unboxed-tuple type, so we can't bind it in the environment). The
underlying problem here is that GHC does transformations like
eta-expanding the tick expressions, and there's nothing we can do to
prevent that.
M ./compiler/ghci/ByteCodeGen.lhs -2 +15
M ./compiler/main/InteractiveEval.hs -5 +9
View patch online:
http://darcs.haskell.org/ghc/_darcs/patches/20090420142525-12142-b7d5bd4930f5f992de05141f55fa5462adb664b6.gz
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