Re: [Haskell-cafe] weird type signature in Arrow Notation

2011-08-04 Thread Brent Yorgey 
On Tue, Aug 02, 2011 at 05:08:33PM -0400, bob zhang wrote:
 hi, all
 testB :: (ArrowChoice t1, Num a1, Num a) = (a - a1 - t2) - t1 a t3
 - t1 a1 t3 - t1 (a, a1) t
 testB f g h = proc (x,y) - do
 if (f x y)then g - x + 1 else h - y + 2
 
 it's very strange that the type of _f_ is (a-a1-t2) which I thought
 should be a - a1 - Bool,
 
 btw, is there any way to get the output of preprocessing using -XArrow
 extensions,
 
 Thanks a lot
 best, bob

Congratulations, you have definitely found a GHC bug!  Note there are
actually two things wrong with testB's type signature: first, t2 ought
to be Bool, as you note.  But even worse, notice that the return type
of the result arrow, t, has nothing to do with any of the other types!
This means that we can use testB along with the (-) instance for
Arrow to construct elements of arbitrary types:

  ghci let anythingYouWant = testB (\x y - False) (const 3) (const 2) (2,2)
  ghci :t anythingYouWant
  anythingYouWant :: t
  ghci anythingYouWant :: Integer
  2
  ghci anythingYouWant :: Int
  2
  ghci anythingYouWant :: Double
  1.0e-323
  ghci anythingYouWant :: Char
  '\STX'
  ghci (anythingYouWant :: (Double - Double) - [Double]) sqrt
  [
  [1]17391 segmentation fault  ghci

whoops!

I'm using GHC 7.0.3, but Daniel Wagner and I also tried it (with the
same results) on GHC 7.2.0rc1 and GHC HEAD.

I wasn't able to find a ticket for this on the GHC bug tracker, I
guess we should file one!

I tried to find a way to get the output of preprocessing using -XArrow
but wasn't able to find one (other than -ddump-ds which gives you the
unoptimized *GHC core* output, which is quite hard to read).

-Brent

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Re: [Haskell-cafe] weird type signature in Arrow Notation

2011-08-04 Thread Sebastian Fischer 
here is a reduced program that still segfaults:

{-# LANGUAGE Arrows #-}

import Control.Arrow

main :: IO ()
main = print segfault

segfault :: [()]
segfault = anythingYouWant ()

anythingYouWant :: a
anythingYouWant = testB False (const ()) ()

testB :: ArrowChoice arrow
  = bool - arrow () () - arrow () anything
testB bool arrow =
  proc () -
do if bool then arrow - ()
   else arrow - ()

Sebastian

On Fri, Aug 5, 2011 at 6:20 AM, Brent Yorgey byor...@seas.upenn.edu wrote:

 On Tue, Aug 02, 2011 at 05:08:33PM -0400, bob zhang wrote:
  hi, all
  testB :: (ArrowChoice t1, Num a1, Num a) = (a - a1 - t2) - t1 a t3
  - t1 a1 t3 - t1 (a, a1) t
  testB f g h = proc (x,y) - do
  if (f x y)then g - x + 1 else h - y + 2
 
  it's very strange that the type of _f_ is (a-a1-t2) which I thought
  should be a - a1 - Bool,
 
  btw, is there any way to get the output of preprocessing using -XArrow
  extensions,
 
  Thanks a lot
  best, bob

 Congratulations, you have definitely found a GHC bug!  Note there are
 actually two things wrong with testB's type signature: first, t2 ought
 to be Bool, as you note.  But even worse, notice that the return type
 of the result arrow, t, has nothing to do with any of the other types!
 This means that we can use testB along with the (-) instance for
 Arrow to construct elements of arbitrary types:

  ghci let anythingYouWant = testB (\x y - False) (const 3) (const 2)
 (2,2)
  ghci :t anythingYouWant
  anythingYouWant :: t
  ghci anythingYouWant :: Integer
  2
  ghci anythingYouWant :: Int
  2
  ghci anythingYouWant :: Double
  1.0e-323
  ghci anythingYouWant :: Char
  '\STX'
  ghci (anythingYouWant :: (Double - Double) - [Double]) sqrt
  [
  [1]17391 segmentation fault  ghci

 whoops!

 I'm using GHC 7.0.3, but Daniel Wagner and I also tried it (with the
 same results) on GHC 7.2.0rc1 and GHC HEAD.

 I wasn't able to find a ticket for this on the GHC bug tracker, I
 guess we should file one!

 I tried to find a way to get the output of preprocessing using -XArrow
 but wasn't able to find one (other than -ddump-ds which gives you the
 unoptimized *GHC core* output, which is quite hard to read).

 -Brent

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Re: [Haskell-cafe] weird type signature in Arrow Notation

2011-08-04 Thread Sebastian Fischer 
I created a ticket with a slightly further simplified program:
http://hackage.haskell.org/trac/ghc/ticket/5380

On Fri, Aug 5, 2011 at 10:10 AM, Sebastian Fischer fisc...@nii.ac.jpwrote:

 here is a reduced program that still segfaults:

 {-# LANGUAGE Arrows #-}

 import Control.Arrow

 main :: IO ()
 main = print segfault

 segfault :: [()]
 segfault = anythingYouWant ()

 anythingYouWant :: a
 anythingYouWant = testB False (const ()) ()

 testB :: ArrowChoice arrow
   = bool - arrow () () - arrow () anything
 testB bool arrow =
   proc () -
 do if bool then arrow - ()
else arrow - ()

 Sebastian

 On Fri, Aug 5, 2011 at 6:20 AM, Brent Yorgey byor...@seas.upenn.eduwrote:

 On Tue, Aug 02, 2011 at 05:08:33PM -0400, bob zhang wrote:
  hi, all
  testB :: (ArrowChoice t1, Num a1, Num a) = (a - a1 - t2) - t1 a t3
  - t1 a1 t3 - t1 (a, a1) t
  testB f g h = proc (x,y) - do
  if (f x y)then g - x + 1 else h - y + 2
 
  it's very strange that the type of _f_ is (a-a1-t2) which I thought
  should be a - a1 - Bool,
 
  btw, is there any way to get the output of preprocessing using -XArrow
  extensions,
 
  Thanks a lot
  best, bob

 Congratulations, you have definitely found a GHC bug!  Note there are
 actually two things wrong with testB's type signature: first, t2 ought
 to be Bool, as you note.  But even worse, notice that the return type
 of the result arrow, t, has nothing to do with any of the other types!
 This means that we can use testB along with the (-) instance for
 Arrow to construct elements of arbitrary types:

  ghci let anythingYouWant = testB (\x y - False) (const 3) (const 2)
 (2,2)
  ghci :t anythingYouWant
  anythingYouWant :: t
  ghci anythingYouWant :: Integer
  2
  ghci anythingYouWant :: Int
  2
  ghci anythingYouWant :: Double
  1.0e-323
  ghci anythingYouWant :: Char
  '\STX'
  ghci (anythingYouWant :: (Double - Double) - [Double]) sqrt
  [
  [1]17391 segmentation fault  ghci

 whoops!

 I'm using GHC 7.0.3, but Daniel Wagner and I also tried it (with the
 same results) on GHC 7.2.0rc1 and GHC HEAD.

 I wasn't able to find a ticket for this on the GHC bug tracker, I
 guess we should file one!

 I tried to find a way to get the output of preprocessing using -XArrow
 but wasn't able to find one (other than -ddump-ds which gives you the
 unoptimized *GHC core* output, which is quite hard to read).

 -Brent

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[Haskell-cafe] weird type signature in Arrow Notation

2011-08-02 Thread bob zhang 
hi, all
testB :: (ArrowChoice t1, Num a1, Num a) = (a - a1 - t2) - t1 a t3
- t1 a1 t3 - t1 (a, a1) t
testB f g h = proc (x,y) - do
if (f x y)then g - x + 1 else h - y + 2

it's very strange that the type of _f_ is (a-a1-t2) which I thought
should be a - a1 - Bool,

btw, is there any way to get the output of preprocessing using -XArrow
extensions,

Thanks a lot
best, bob


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