If, as I understand it, you are relying on the fact that seq's first
argument is evaluted before its second, then you really want pseq
rather than seq.
In GHC we provide a way to do what you want (pseq), I'm just not
convinced it should be the required behaviour of seq.
Whilst looking for something else, I have discovered that the official
list of changes from Haskell 1.2 to Haskell 1.3 has this explicit
statement:
"The seq function evaluates its first argument before returning the
second one."
http://haskell.org/definition/from12to13.html
In addition, the 1.3 and 1.4 Reports, in describing how seq should be
understood for any particular type, states:
"The _case_ is used to force evaluation of the first argument to `seq`
before returning the second argument."
The Haskell'98 committee decided to remove the Eval class (that had
seq as one of its methods), see http://www.cs.chalmers.se/~rjmh/Haskell/Messages/Decision.cgi?id=204
I assume that it was simply inattention whilst editing the Report
text, that caused the removal of the official requirement that seq
evaluate its first argument before its second, because I can find no
discussion by the committee that suggested such an important change.
If you can point me to the committee discussion that led to changing
this requirement, I would be grateful.
Regards,
Malcolm
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