#1349: Generalise the ! and UNPACK mechanism for data types, to unpack function
arguments
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Reporter: simonpj | Owner:
Type: task | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler | Version: 6.6.1
Severity: normal | Resolution:
Keywords: | Difficulty: Unknown
Testcase: | Architecture: Unknown
Os: Unknown |
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Comment (by Isaac Dupree):
Strictness annotations in function results don't make sense (for the same
reason `id` is strict -- function results are "already WHNF-strict" as
much as it makes sense), and they're already lifted (in the sense that
they can possibly produce _|_) even for unboxed result types (e.g. {{{bot
:: () -> Int#; bot x = bot x}}}). But unboxing a result-tuple can result
in a loss of sharing, so in
{{{
newtype State s a
= State
{ runState' :: s -> (# a, s #) }
}}}
the unboxedness of the tuple really is significant for efficiency reasons,
to tell GHC that it doesn't need to preserve sharing. See
http://www.nabble.com/there-isn%27t-any-difference%2C-is-there%2C-with-
unboxed-tuples--to14629139.html
So I also want a function-result-syntax of UNPACK, presumably without an
intervening meaningless strictness annotation:
{{{
newtype State s a
= State
{ runState' :: s -> {-# UNPACK #-} ( a, s ) }
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1349#comment:4>
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