patch applied (ghc): Improve the treatment of 'seq' (Trac #2273)

[Don Stewart]

simonpj:
> Fri May 16 01:51:49 PDT 2008  simonpj at microsoft.com
>   * Improve the treatment of 'seq' (Trac #2273)
>   
>   Trac #2273 showed a case in which 'seq' didn't cure the space leak
>   it was supposed to.  This patch does two things to help
>   
>   a) It removes a now-redundant special case in Simplify, which
>      switched off the case-binder-swap in the early stages.  This
>      isn't necessary any more because FloatOut has improved since
>      the Simplify code was written.  And switching off the binder-swap
>      is harmful for seq.
>   
>   However fix (a) is a bit fragile, so I did (b) too:
>   
>   b) Desugar 'seq' specially.  See Note [Desugaring seq (2)] in DsUtils
>      This isn't very robust either, since it's defeated by abstraction, 
>      but that's not something GHC can fix; the programmer should use
>      a let! instead.
>   
> 

By let! do you mean

    let !x = ...

?

-- Don