Re: [Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
f :: (Show a, Ord b) = (a - String, b - b - Bool)
f = let commond_definitions = undefined in
let f1 = id.show
f2 x = ( x)
in
(f1, f2)
From: Ting Lei tin...@hotmail.com
To: haskell-cafe@haskell.org
Cc:
Date: Wed, 28 Mar 2012 23:42:30 -0700
Subject: [Haskell-cafe] a code that cannot compile with or without
NoMonomorphismRestriction
Hi
I have met a piece of code that cannot be compiled whether I add or remove
the NoMonomorphismRestriction flag (as of GHC 7.0.4, Haskell platform
2011.4.0.0).
I have extracted a minimal example below:
{-# LANGUAGE NoMonomorphismRestriction #-}
(f1, f2) =
let commond_definitions = undefined in
let f1 = id.show
f2 x = ( x)
in
(f1, f2)
I needed this format because there are many shared definitions in
common_definitions for f1 and f2, and I want to keep them local.
If I compile them with NoMonomorphismRestriction, I get:
D:\work\test.hs:7:8:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `f1'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
In the expression: f1
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
D:\work\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none.
If I comment out
-- {-# LANGUAGE NoMonomorphismRestriction #-}
I get:
D:\work\hsOcaml\test.hs:4:17:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `show'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the second argument of `(.)', namely `show'
In the expression: id . show
In an equation for `f1': f1 = id . show
D:\work\hsOcaml\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none.
Can anyone show me why this does not work and how to fix it (e.g. by
adding type signature as the error message suggested)?
I tried to add type signature by couldn't figure out the right way of
doing it.
Thanks in advance!
Ting
Denis Moskvin
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[Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
Hi I have met a piece of code that cannot be compiled whether I add or remove
the NoMonomorphismRestriction flag (as of GHC 7.0.4, Haskell platform
2011.4.0.0).I have extracted a minimal example below: {-# LANGUAGE
NoMonomorphismRestriction #-}
(f1, f2) =
let commond_definitions = undefined in
let f1 = id.show
f2 x = ( x)
in
(f1, f2) I needed this format because there are many shared definitions
in common_definitions for f1 and f2, and I want to keep them local. If I
compile them with NoMonomorphismRestriction, I get:
D:\work\test.hs:7:8:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `f1'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
In the expression: f1
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)D:\work\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none. If I comment out -- {-# LANGUAGE
NoMonomorphismRestriction #-}
I get:
D:\work\hsOcaml\test.hs:4:17:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `show'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the second argument of `(.)', namely `show'
In the expression: id . show
In an equation for `f1': f1 = id . showD:\work\hsOcaml\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none. Can anyone show me why this does not work and how
to fix it (e.g. by adding type signature as the error message suggested)?I
tried to add type signature by couldn't figure out the right way of doing it.
Thanks in advance! Ting ___
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Re: [Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
Ting Lei tin...@hotmail.com writes: (f1, f2) = let commond_definitions = undefined in let f1 = id.show f2 x = ( x) in (f1, f2) I think the type signatures should be: f1 :: Show a = a - String and f2 :: Ord b = b - b - Bool When I define these separately, this works: f1 :: Show a = a - String f1 = id . show f2 :: Ord b = b - b - Bool f2 = flip () But when I define them as a pair f1 :: Show a = a - String f2 :: Ord b = b - b - Bool (f1,f2) = (id . show, flip ()) I get an error message: Line 9: 1 error(s), 0 warning(s) Couldn't match expected type `forall a. Show a = a - String' with actual type `a - String' When checking that `f1' has the specified type `forall a1. Show a1 = a1 - String' Defining the pair at once works: p :: (Show a, Ord b) = (a - String, b - b - Bool) p = (id . show, flip ()) I guess that didn't help a lot, somebody with deeper GHC-fu than me will have to step in. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
Ketil Malde wrote: Ting Lei tin...@hotmail.com writes: (f1, f2) = let commond_definitions = undefined in let f1 = id.show f2 x = ( x) in (f1, f2) I think the type signatures should be: f1 :: Show a = a - String and f2 :: Ord b = b - b - Bool When I define these separately, this works: f1 :: Show a = a - String f1 = id . show f2 :: Ord b = b - b - Bool f2 = flip () But when I define them as a pair f1 :: Show a = a - String f2 :: Ord b = b - b - Bool (f1,f2) = (id . show, flip ()) I get an error message: Line 9: 1 error(s), 0 warning(s) Couldn't match expected type `forall a. Show a = a - String' with actual type `a - String' When checking that `f1' has the specified type `forall a1. Show a1 = a1 - String' Defining the pair at once works: p :: (Show a, Ord b) = (a - String, b - b - Bool) p = (id . show, flip ()) I guess that didn't help a lot, somebody with deeper GHC-fu than me will have to step in. The problem is that f1 and f2 are polymorphic functions. To put polymorphic functions in a pair, you need *impredicative polymorphism*. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
I think the error message tell you how to fix:
use -XNoMonomorphismRestriction
One approach is add following line into top of your hs file and it works for me.
{-# LANGUAGE NoMonomorphismRestriction #-}
Regarding the deeper reason, I think you would be able to find via GHC
user guide and google.
-Haisheng
On Thu, Mar 29, 2012 at 2:42 PM, Ting Lei tin...@hotmail.com wrote:
Hi
I have met a piece of code that cannot be compiled whether I add or remove
the NoMonomorphismRestriction flag (as of GHC 7.0.4, Haskell platform
2011.4.0.0).
I have extracted a minimal example below:
{-# LANGUAGE NoMonomorphismRestriction #-}
(f1, f2) =
let commond_definitions = undefined in
let f1 = id.show
f2 x = ( x)
in
(f1, f2)
I needed this format because there are many shared definitions in
common_definitions for f1 and f2, and I want to keep them local.
If I compile them with NoMonomorphismRestriction, I get:
D:\work\test.hs:7:8:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `f1'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
In the expression: f1
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
D:\work\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none.
If I comment out
-- {-# LANGUAGE NoMonomorphismRestriction #-}
I get:
D:\work\hsOcaml\test.hs:4:17:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `show'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test.hs:2:2)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the second argument of `(.)', namely `show'
In the expression: id . show
In an equation for `f1': f1 = id . show
D:\work\hsOcaml\test.hs:7:12:
Ambiguous type variable `a1' in the constraint:
(Ord a1) arising from a use of `f2'
Possible cause: the monomorphism restriction applied to the following:
f2 :: a1 - a1 - Bool (bound at D:\work\hsOcaml\test.hs:2:6)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the expression: f2
In the expression: (f1, f2)
In the expression:
let
f1 = id . show
f2 x = ( x)
in (f1, f2)
Failed, modules loaded: none.
Can anyone show me why this does not work and how to fix it (e.g. by adding
type signature as the error message suggested)?
I tried to add type signature by couldn't figure out the right way of doing
it.
Thanks in advance!
Ting
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Re: [Haskell-cafe] a code that cannot compile with or without NoMonomorphismRestriction
Ketil, Thanks for the response. It seems that defining them as a pair only
postphones the error.GHC will give an error when you extract the components of
the pair, no matter whether you addthe NoMonomorphismRestriction flag or not.
--{-# LANGUAGE NoMonomorphismRestriction #-}p :: (Show a, Ord b) = (a -
String, b - b - Bool)
p = (id . show, flip ())f1 = fst p
f2 = snd p---Without NoMonomorphismRestriction, I got:
D:\work\test1.hs:6:10:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `p'
Possible cause: the monomorphism restriction applied to the following:
f1 :: a0 - String (bound at D:\work\hsOcaml\test1.hs:6:1)
Probable fix: give these definition(s) an explicit type signature
or use -XNoMonomorphismRestriction
In the first argument of `fst', namely `p'
In the expression: fst p
In an equation for `f1': f1 = fst pD:\work\hsOcaml\test1.hs:6:10:
Ambiguous type variable `b0' in the constraint:
(Ord b0) arising from a use of `p'
Probable fix: add a type signature that fixes these type variable(s)
.. Failed, modules loaded: none. --With
NoMonomorphismRestriction, I got:
D:\work\test1.hs:6:10:
Ambiguous type variable `b0' in the constraint:
(Ord b0) arising from a use of `p'
Probable fix: add a type signature that fixes these type variable(s)
In the first argument of `fst', namely `p'
In the expression: fst p
In an equation for `f1': f1 = fst pD:\work\test1.hs:7:10:
Ambiguous type variable `a0' in the constraint:
(Show a0) arising from a use of `p'
Probable fix: add a type signature that fixes these type variable(s)
In the first argument of `snd', namely `p'
In the expression: snd p
In an equation for `f2': f2 = snd p
Failed, modules loaded: none. Thanks,
Ting From: ke...@malde.org
To: tin...@hotmail.com
CC: haskell-cafe@haskell.org
Subject: Re: [Haskell-cafe] a code that cannot compile with or without
NoMonomorphismRestriction
Date: Thu, 29 Mar 2012 12:27:04 +0200
Ting Lei tin...@hotmail.com writes:
(f1, f2) =
let commond_definitions = undefined in
let f1 = id.show
f2 x = ( x)
in
(f1, f2)
I think the type signatures should be:
f1 :: Show a = a - String
and
f2 :: Ord b = b - b - Bool
When I define these separately, this works:
f1 :: Show a = a - String
f1 = id . show
f2 :: Ord b = b - b - Bool
f2 = flip ()
But when I define them as a pair
f1 :: Show a = a - String
f2 :: Ord b = b - b - Bool
(f1,f2) = (id . show, flip ())
I get an error message:
Line 9: 1 error(s), 0 warning(s)
Couldn't match expected type `forall a. Show a = a - String'
with actual type `a - String'
When checking that `f1'
has the specified type `forall a1. Show a1 = a1 - String'
Defining the pair at once works:
p :: (Show a, Ord b) = (a - String, b - b - Bool)
p = (id . show, flip ())
I guess that didn't help a lot, somebody with deeper GHC-fu than me will
have to step in.
-k
--
If I haven't seen further, it is by standing in the footprints of giants
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