#1349: Generalise the ! and UNPACK mechanism for data types, to unpack function
arguments
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: task | Status: new
Priority: normal | Milestone: 6.12.3
Component: Compiler | Version: 6.6.1
Keywords: | Difficulty: Unknown
Os: Unknown/Multiple | Testcase:
Architecture: Unknown/Multiple | Failure: None/Unknown
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Comment(by tibbe):
It's a bit tricky to come up with a good example as inlining seems to
remove the problem for simple cases. Here's an attempt. Given the module:
{{{
module Cont (run) where
type Cont = (Int -> Int) -> Int -> Int
g :: Cont
g k n = let n' = n + 1 in n' `seq` k n'
loop :: Int -> Cont
loop 0 = id
loop n = g . loop (n - 1)
run = loop 10 id
}}}
we get the Core
{{{
Cont.$wloop :: Int#
-> (Int -> Int)
-> Int
-> Int
Cont.$wloop =
\ (ww_shX :: Int#) ->
case ww_shX of ds_Xhe {
__DEFAULT ->
let {
g_si5 :: (Int -> Int)
-> Int
-> Int
g_si5 = Cont.$wloop (-# ds_Xhe 1) } in
\ (x_ahg :: Int -> Int) ->
let {
k_si7 [ALWAYS Just L] :: Int -> Int
k_si7 = g_si5 x_ahg } in
\ (n_adm :: Int) ->
case n_adm of _ { I# x1_ahv ->
k_si7 (I# (+# x1_ahv 1))
};
0 -> id @ (Int -> Int)
}
Cont.run :: Int -> Int
Cont.run = Cont.$wloop 10 (id @ Int)
}}}
However, manual unboxing
{{{
{-# LANGUAGE MagicHash #-}
module Cont2 (run) where
import GHC.Prim
import GHC.Base
type Cont = (Int# -> Int) -> Int# -> Int
g :: Cont
g k n = k (n +# 1#)
loop :: Int -> Cont
loop 0 = id
loop n = g . loop (n - 1)
run = loop 10 (\i -> (I# i))
}}}
gives
{{{
Cont2.$wloop :: Int#
-> (Int# -> Int)
-> Int#
-> Int
Cont2.$wloop =
\ (ww_shs :: Int#) ->
case ww_shs of ds_XgX {
__DEFAULT ->
let {
g_shA :: (Int# -> Int)
-> Int#
-> Int
g_shA = Cont2.$wloop (-# ds_XgX 1) } in
\ (x_agX :: Int# -> Int) ->
let {
k_shC [ALWAYS Just L] :: Int# -> Int
k_shC = g_shA x_agX } in
\ (n_adn :: Int#) -> k_shC (+# n_adn 1);
0 -> id @ (Int# -> Int)
}
Cont2.run :: Int# -> Int
Cont2.run = Cont2.$wloop 10 I#
}}}
I'd like to be able to express that `Cont`'s first parameter (of type `Int
-> Int`) is strict in its first (and only) arguments and that I want it
unboxed.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1349#comment:21>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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