h the parse function returns one. It just ignores
> the ParseFailed case. I was going to try fixing it and send a pull
> request when I ran into the Cabal 2.* problem.
>
> On Wed, Jul 26, 2017 at 7:15 AM, Ben Gamari <b...@smart-cactus.org>
> wrote:
> >
> > Wolfgang
Am Samstag, den 22.07.2017, 23:03 -0400 schrieb Ben Gamari:
> In addition, there are a number of new features,
>
> * A new, more type-safe type reflection mechanism
>
> * The long-awaited Backpack module system
>
> * Deriving strategies to disambiguate between GHC's various instance
>
Hi!
The base package contains the module Data.Type.Equality, which contains
the type (:~:) for homogeneous equality. I was a bit surprised that
there is no type for heterogeneous equality there. Is there such a type
somewhere else in the standard library?
I tried to define a type for
gt;
>
> In short, fundeps and type family dependencies only add extra
> unification constraints, which may help to resolve ambiguous
> types. They don’t provide evidence. That's not to say that they
> couldn't. But you'd need to extend System FC, GHC's core language, to
> do so.
Hi!
Injective type families as supported by GHC 8.0.1 do not behave like I
would expect them to behave from my intuitive understanding.
Let us consider the following example:
> {-# LANGUAGE RankNTypes, TypeFamilyDependencies #-}
>
> class C a where
>
> type T a = b | b -> a
>
> instance
Am Sonntag, den 18.06.2017, 12:02 -0700 schrieb wren romano:
> > > {-# LANGUAGE Rank2Types, TypeFamilies #-}
> > >
> > > import GHC.Exts (Constraint)
> > >
> > > type family F a b :: Constraint
> > >
> > > data T b c = T
> > >
> > > f :: (forall b . F a b => T b c) -> a
> > > f _ = undefined
>
Hi!
In my previous e-mail, I showed some code that uses the Constraint kind.
I forgot to enable the ConstraintKinds extension though, but GHC 8.0.1
did not complain. Is this a bug?
All the best,
Wolfgang
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Hi!
Today I encountered for the first time the notion of an “untouchable”
type variable. I have no clue what this is supposed to mean. A minimal
example that exposes my problem is the following:
> {-# LANGUAGE Rank2Types, TypeFamilies #-}
>
> import GHC.Exts (Constraint)
>
> type family F a b
://ghc.haskell.org/trac/ghc/ticket/10009 might be the same
regression (fixed in HEAD)
Regards,
Adam
On Tue, Jun 2, 2015 at 12:28 PM, Wolfgang Jeltsch
g9ks1...@acme.softbase.org wrote:
Hi,
the following (contrived) code is accepted by GHC 7.8.3
Hi,
the following (contrived) code is accepted by GHC 7.8.3, but not 7.10.1:
{-# LANGUAGE TypeFamilies #-}
type family F a :: *
type family G b :: *
x :: G (F a) ~ a = F a
x = undefined
GHC 7.10.1 reports:
Could not deduce (F a0 ~ F a)
from the context (G (F a) ~ a)
bound by
Am Freitag, den 15.08.2014, 23:10 +0300 schrieb Wolfgang Jeltsch:
Hi,
the module Control.Arrow declares a set of rules for the Arrow class. It
is marked “Trustworthy”, probably to allow these rules to actually fire.
Now these rules are only correct for class instances that actually
Hi,
the documentation of System.Mem.Weak under
http://hackage.haskell.org/package/base-4.7.0.1/docs/System-Mem-Weak.html
says the following:
It is not guaranteed that a finalizer will eventually run, and no
attempt is made to run outstanding finalizers when the program exits.
In which
of
GHC.Prim indeed says Safe Inferred), but not a real bug.
Let me know if you see otherwise!
Thanks,
Richard
On Aug 16, 2014, at 6:06 PM, Wolfgang Jeltsch g9ks1...@acme.softbase.org
wrote:
Hi,
thank you for these links.
Still, it is interesting that also in GHC 7.8 you can
abstraction expectations that are defeated through the use of `coerce`.
I would strongly welcome a proposal for how to make `coerce`, and hence
GeneralizedNewtypeDeriving, to be considered Safe for 7.10.
Richard
On Aug 15, 2014, at 4:04 PM, Wolfgang Jeltsch g9ks1...@acme.softbase.org
wrote
Hi,
I would expect the function
coerce :: Coercible a b = a - b
to be safe in the sense of Safe Haskell. However, the Data.Coerce module
is marked “Unsafe”. The coerce function is also available via GHC.Exts
and GHC.Prim. The former module is marked “Unsafe”, but the latter is
Hi,
the module Control.Arrow declares a set of rules for the Arrow class. It
is marked “Trustworthy”, probably to allow these rules to actually fire.
Now these rules are only correct for class instances that actually
satisfy the arrow laws. If the author of another module defines an
instance of
Am Freitag, den 13.07.2012, 13:40 +0100 schrieb Ross Paterson:
Remember that there is a \ in arrow notation in addition to proc.
So one might expect any abbreviation for \x - case x of {...}
to mean the same \ thing in arrow notation too.
I completely agree. I had forgotten about the \ in
Am Montag, den 16.07.2012, 21:26 +0300 schrieb Wolfgang Jeltsch:
Am Freitag, den 13.07.2012, 13:40 +0100 schrieb Ross Paterson:
Remember that there is a \ in arrow notation in addition to proc.
So one might expect any abbreviation for \x - case x of {...}
to mean the same \ thing in arrow
Am Donnerstag, den 12.07.2012, 13:38 -0400 schrieb Cale Gibbard:
Personally I don't see why everyone appears to prefer the syntax with
\ in it over just the obvious case section syntax which was originally
proposed.
case of { ... }
looks much better to me than
\case of { ... }
and
Am Freitag, den 13.07.2012, 06:57 -0700 schrieb Donn Cave:
Quoth Cale Gibbard:
Personally I don't see why everyone appears to prefer the syntax with
\ in it over just the obvious case section syntax which was originally
proposed.
case of { ... }
...
Does anyone else agree?
Yes.
Am Dienstag, den 10.07.2012, 08:53 +0100 schrieb Simon Marlow:
On 09/07/2012 17:32, Mikhail Vorozhtsov wrote:
Would you still expect tuples for \case if you didn't see the way
`case x, y of ...` was implemented (or thought that it is a
primitive construct)?
Yes, I still think it's
Am Dienstag, den 10.07.2012, 06:53 + schrieb Simon Peyton-Jones:
I strongly favor a solution where lambda-case expressions start with \,
because this can be generalized to proc expressions from arrow syntax
simply by replacing the \ with proc.
[…]
I think it's very helpful if
Am Samstag, den 07.07.2012, 00:08 -0400 schrieb Tyson Whitehead:
I've thought some more about this and it seems to me that there are
two ways people might intuitively think about doing grouping via
indentation.
1 - the first item is on the same line and subsequent ones are lined
up with
Am Montag, den 09.07.2012, 21:04 +0700 schrieb Mikhail Vorozhtsov:
Could you express your opinion on the case comma sugar, i.e.
case x, y of
P1, P2 - ...
P3, P4 - ...
as sugar for
case (# x, y #) of
(# P1, P2 #) - ...
(# P3, P4 #) - ...
and respectively
\case
Am Montag, den 09.07.2012, 10:20 -0600 schrieb Chris Smith:
Right, it seems to me that there are basically three reasonable proposals
here:
1. \ of with multiple arguments. This is consistent with existing
layout, and seems like a nice generalization of lambda syntax.
2. case of with a
Am Donnerstag, den 22.12.2011, 00:02 +0100 schrieb Bas van Dijk:
On 21 December 2011 19:29, Ian Lynagh ig...@earth.li wrote:
* There is a new feature constraint kinds (-XConstraintKinds):
http://www.haskell.org/ghc/dist/stable/docs/html/users_guide/constraint-kind.html
I'm trying
Am Montag, den 07.11.2011, 21:41 + schrieb Barney Hilken:
The problem with this approach is that different labels do not have
different representations at the value level.
I think this is an advantage, because it means you don't have to carry
this stuff about at runtime.
This
Am Montag, den 07.11.2011, 23:30 + schrieb Simon Peyton-Jones:
Wolfgang
Is there a wiki page giving a specific, concrete design for the
proposal you advocate? Something at the level of detail of
http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields?
Well, I don’t
Am Freitag, den 04.11.2011, 20:16 -0400 schrieb wagne...@seas.upenn.edu:
Quoting wagne...@seas.upenn.edu:
Quoting Wolfgang Jeltsch g9ks1...@acme.softbase.org:
this code is accepted by GHC 7.0.4:
snip
However, this one isn?t:
{-# LANGUAGE ImpredicativeTypes #-}
polyId
Am Montag, den 07.11.2011, 14:49 +0200 schrieb Wolfgang Jeltsch:
Am Freitag, den 04.11.2011, 20:16 -0400 schrieb wagne...@seas.upenn.edu:
The first thing to observe is that, ideally, the following two types
would mean slightly different things:
polyId :: forall b. (forall a. Maybe
Am Montag, den 07.11.2011, 17:53 + schrieb Barney Hilken:
Here is my understanding of the current state of the argument:
Instead of Labels, there will be a new kind String, which is not a
subkind of *, so its elements are not types. The elements of String
are strings at the type level,
Am Montag, den 07.11.2011, 18:16 +0100 schrieb Claus Reinke:
I am unsure which of this list of proposals you are referring to. The
URL you quote is this
http://hackage.haskell.org/trac/haskell-prime/wiki/FirstClassLabels
That sounds familiar, I think I wrote that when I was younger;-)
Hello,
this code is accepted by GHC 7.0.4:
{-# LANGUAGE ImpredicativeTypes #-}
polyId :: (forall a. a) - a
polyId x = x
polyIdMap :: [forall a. a] - [forall a. a]
polyIdMap xs = fmap polyId xs
However, this one isn’t:
{-# LANGUAGE ImpredicativeTypes #-}
polyId :: (forall a. Maybe
Am Freitag, den 30.09.2011, 19:28 +0200 schrieb George Giorgidze:
Basically the idea is to treat list literals like:
[1,2,3]
as
fromList [1,2,3]
where
class IsList l where
type Item l
fromList :: [Item l] - l
Could we *please* not have classes whose names start with “Is”? We
Am Donnerstag, den 20.01.2011, 23:25 +0900 schrieb 山本和彦:
I'm asking why GHC breaks backward compatibility (e.g.
FlexibleInstances and BangPatterns) and why maintainers of packages
should do boring fixes. What are benefits of such overhead?
Hi,
what are the changes in GHC wrt.
Hello guys,
are you following this Haskell Cafe thread:
http://www.mail-archive.com/haskell-c...@haskell.org/msg72300.html
Seems that you can do ugly things with GHC’s current implementation of
generalized newtype deriving. For example, you can easily construct sets with
corrupted
Am Freitag, 30. Oktober 2009 10:51:37 schrieb Simon Peyton-Jones:
Friends
One more update about GHC 6.12, concerning impredicative polymorphism.
GHC has had an experimental implementation of impredicative polymorphism
for a year or two now (flag -XImpredicativePolymorphism). But
a)
Am Samstag, 27. Juni 2009 12:44 schrieb Niklas Broberg:
Hi all,
Following the discussion on the use of 'forall' and extensions that
use it [1], I would hereby like to propose that the
ExistentialQuantification extension is deprecated.
My rationale is as follows. With the introduction of
Am Samstag, 23. Mai 2009 21:58 schrieb Dean Herington:
I'm trying to give Grapefruit a try. I installed it as described in
section 4.1 of http://www.haskell.org/haskellwiki/Grapefruit. When I
tried to run the Simple.hs example, I got the problem shown below.
Any ideas?
My machine is
Am Montag, 29. Dezember 2008 12:54 schrieb Simon Peyton-Jones:
What a great bug -- I would never have predicted it, but in retrospect it
makes perfect sense. Record selectors had better get fixed.
Can I read somewhere about what caused this bug? What is its trac URL?
Best wishes,
Wolfgang
Am Montag, 15. Dezember 2008 02:17 schrieb Ben Horsfall:
I have a type family
class Lang term where
data Token term :: *
with
instance Lang Term where
newtype Token Term = T String
I can't work out how to export the type constructor T from the module,
unless I make no explict
Am Samstag, 11. Oktober 2008 09:36 schrieb Duncan Coutts:
All,
We've been using the cabal-install build reporting stuff to get more
detailed info on build failures with ghc-6.10 vs 6.8. cabal-install
generates these build-reports.log files and individual log files for
each build.
Hello,
I built GHC 6.10.0.20080927 on Debian GNU/Linux for i386. At the end of the
build process I got numerous warnings of the form “could not find link
destinations for: […]”. Is this intensional?
Best wishes,
Wolfgang
___
Glasgow-haskell-users
Am Dienstag, 23. September 2008 19:07 schrieben Sie:
{-# LANGUAGE GADTs, MultiParamTypeClasses, FunctionalDependencies #-}
data GADT a where
GADT :: GADT ()
class Class a b | a - b
instance Class () ()
fun :: (Class a b) = GADT a - b
fun GADT = ()
I’d expect this to
Am Mittwoch, 24. September 2008 15:11 schrieb Ian Lynagh:
On Wed, Sep 24, 2008 at 12:55:29PM +0200, Wolfgang Jeltsch wrote:
I thought, someone said that with the new typing machinery in GHC 6.10,
more functional dependency programs are accepted because functional
dependencies are handled
Hello Simon,
thank you for your extensive answer!
I think, I’ll try to work around the fundep deficiencies and if that doesn’t
work, switch to type families.
But your answer raised further questions/comments:
class (F a ~ b) = C a b
type family F a
(Note for 6.10 users:
Am Montag, 22. September 2008 08:52 schrieb Yitzchak Gale:
[…]
Unfortunately, the so-called generic Linux binary distribution
package for GHC 6.8.3 does not work on the current, up-to-date
Debian stable distribution because it is too old.
GHC 6.8.2 worked for me (on i386).
[…]
Best
Am Dienstag, 23. September 2008 18:19 schrieben Sie:
On Tue, Sep 23, 2008 at 6:07 PM, Wolfgang Jeltsch
[EMAIL PROTECTED] wrote:
Hello,
please consider the following code:
{-# LANGUAGE GADTs, MultiParamTypeClasses, FunctionalDependencies #-}
data GADT a where
GADT :: GADT
Am Donnerstag, 11. September 2008 00:09 schrieben Sie:
If an FRP library provides first-class signals then often the problem
arises that these are actually signal generators—their behavior might
depend on the time they are started. To get rid of this deficiency, my
signal types now have an
Hello,
I have some code giving me the error message: “GADT pattern match in non-rigid
context for … Tell GHC HQ if you'd like this to unify the context”. I
reduced my code to the following example which still gives this error
message:
data T a b where
C :: T a [b]
f :: (forall a'.
Am Dienstag, 19. Februar 2008 11:36 schrieb Wolfgang Jeltsch:
Am Montag, 18. Februar 2008 19:46 schrieb Carlos Gomez A.:
hi, my name is carlos
I need information for correct installor
what are dependencies on ghc ?
I have a Debian System.
Always use your distribution’s
Am Dienstag, 19. Februar 2008 12:03 schrieb Wolfgang Jeltsch:
Am Dienstag, 19. Februar 2008 11:36 schrieb Wolfgang Jeltsch:
Am Montag, 18. Februar 2008 19:46 schrieb Carlos Gomez A.:
hi, my name is carlos
I need information for correct installor
what are dependencies on ghc
Hello,
what are the plans for implicit parameters? Will GHC continue to support them
or could it be that they will be removed at some time?
I think that implicit parameters can be very useful for implementing global
variables as described in http://www.cs.chalmers.se/~rjmh/Globals.ps.
Am Montag, 28. Januar 2008 18:52 schrieb Albert Y. C. Lai:
On GHC version-specific download pages (e.g.,
http://www.haskell.org/ghc/download_ghc_682.html), under Source
Distribution, it would reduce a major confusion of the form I built GHC
from source, now I use it, it says Network.CGI not
Am Sonntag, 6. Januar 2008 13:37 schrieb Adrian Hey:
It's the GT class here..
Short remark: Wouldn’t a longer, more descriptive identifier be better?
Best wishes,
Wolfgang
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Am Sonntag, 23. Dezember 2007 13:35 schrieb Isaac Dupree:
GHC optimizes less effectively when parts of a program are in different
modules, or are exported from a module.
By the way, does GHC do cross-package optimization (not just cross-module
optimization within packages)?
[…]
Best wishes,
Am Montag, 17. Dezember 2007 20:32 schrieb Paulo J. Matos:
Hello all,
I've came across a problem which would be best implemented if I could
define what I think to be a Type Relation. Let's consider classes as
being type properties.
When you say:
class Num a where
(+) :: a - a - a
...
Am Donnerstag, 6. Dezember 2007 10:43 schrieb Bernd Brassel:
Is it already a known problem that the preprocessor cannot cope with the
whole set of possible string declarations?
Yes, it is. There is cpphs (http://www.cs.york.ac.uk/fp/cpphs/) as an
alternative.
[…]
Best wishes,
Wolfgang
Am Mittwoch, 5. Dezember 2007 13:43 schrieb Luis Cabellos:
Hi,
I have a question, what's the best way to program?
- put all the signatures in the Haskell Code?
- Only put the type signatures needed to compile (like monomorphism errors
or ambiguous signature)?
Until now, I prefer the
Am Mittwoch, 5. Dezember 2007 17:05 schrieb Simon Peyton-Jones:
[…]
Anyway, while on this subject, I am considering making the following
change:
make all operator symbols into type constructors
(currently they are type variables)
This would be highly problematic!
Am Montag, 3. Dezember 2007 13:38 schrieben Sie:
[…]
I just thought it would be nice to have all installed libraries together
because that would facilitate deciding whether I use something from the
containers package, or the collections package or edison.
Do you mean you want a combined
Am Freitag, 30. November 2007 15:23 schrieb Daniel Fischer:
Question 2: When I build a package via Cabal, is there a way to merge the
documentation into the installed library docs (and if yes, how do I do it)?
I think, if you do
runhaskell Setup.[l]hs haddock
before
runhaskell
Am Dienstag, 27. November 2007 19:21 schrieb Alex Jacobson:
Simon, I think we've been trying to be too clever...
The simple question is: for a given extension, what is the risk of
leaving it turned on by default?
The risk is that one thinks that one’s program is Haskell-98-compliant while
it
Am Mittwoch, 21. November 2007 19:38 schrieb Alex Jacobson:
Isn't use of the extensions detectable by the compiler?
So you want extension inference. ;-)
[…]
In any case, I'm pretty sure the correct answer is not 50 language
pragmas with arbitrary spellings for various language features at
Am Donnerstag, 22. November 2007 02:07 schrieb Alex Jacobson:
Duncan Coutts wrote:
On Wed, 2007-11-21 at 19:26 -0500, Alex Jacobson wrote:
Ok, I'm game to default to haskell98 in the presence of ambiguity, but
in most cases the extension involves new syntax and that should be
enough.
Am Dienstag, 20. November 2007 22:35 schrieb Alex Jacobson:
[…]
{-# LANGUAGE TemplateHaskell, FlexibleInstances,
OverlappingInstances, UndecidableInstances, CPP,
ScopedTypeVariables, PatternSignatures, GADTs,
PolymorphicComponents, FlexibleContexts,
Am Mittwoch, 21. November 2007 15:03 schrieb Serge D. Mechveliani:
Dear GHC developers,
when compiling the function f x = if x them False else True
ghc-8.8.1 reports:parse error on input `else' .
When there is a large expession after `them', it is sometimes
difficult to locate a
Hello,
please consider the following program:
main = putChar 'A' main
I load this into GHCi, enter :step main, followed by :step and a second :step.
Although I would expect to get the As in the output step by step, GHCi now
hangs inside the infinite loop. Is this intentional? To me,
Am Dienstag, 20. November 2007 22:15 schrieb Alex Jacobson:
.ehs stands for extended haskell and encapsulates the 90% case of people
just wanting -fglasgow-exts with a minimum of fuss.
Having a filetype seesm better than the alternatives of either adding
boilerplate language/options pragmas
Am Freitag, 9. November 2007 08:24 schrieb Lennart Augustsson:
I'd like to second that. 6.8 is quite an improvement. Well done!
-- Lennart
So those language shootouts should be updated to use GHC 6.8.1 for their
benchmarks.
Best wishes,
Wolfgang
Am Freitag, 19. Oktober 2007 11:32 schrieben Sie:
[…]
| In fact, after thinking and experimenting I came to the conclusion that
| it’s probably just not possible to define a type function TypeEqTF t1 t2
| which for *all* types t1 and t2 yields True or False, depending on
| whether t1 and t2
Am Montag, 10. Oktober 2005 08:38 schrieb Tomasz Zielonka:
On 10/10/05, Ketil Malde [EMAIL PROTECTED] wrote:
Tomasz Zielonka [EMAIL PROTECTED] writes:
Because of this long syntax and comand-line completion I've even once
lost the source code. I forgot to remove the .hs at the end of line:
Am Montag, 10. Oktober 2005 11:55 schrieb Niklas Broberg:
[...]
Using a shell script is a possible work-around, but certainly not
*the* solution. If there is no real reason for ghc to spit out a.out
files, then surely choosing the exe name from the main input file
would simplify a
Hello,
http://haskell.org/ghc/docs/latest/html/libraries/base/
System.IO.Unsafe.html#v%3AunsafePerformIO
talks about what optimizations you should disable if you apply unsafePerformIO
to an action which contains side effects. These are:
* inlining of functions which call
Am Mittwoch, 27. Juli 2005 21:39 schrieben Sie:
Wolfgang Jeltsch [EMAIL PROTECTED] writes:
But how do I switch off let-floating?
-fno-full-laziness, I believe.
I just tried using this flag. Result: GHC 6.2.2 doesn't recognize it. :-(
--sigbjorn
Regards,
Wolfgang
Am Donnerstag, 28. Juli 2005 16:42 schrieb Peter Simons:
Wolfgang Jeltsch writes:
where is this switch documented?
http://haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html
#id3128647
Peter
Thank you.
Wolfgang
___
Glasgow-haskell
Am Donnerstag, 28. Juli 2005 16:45 schrieben Sie:
On Thu, 28 Jul 2005, Wolfgang Jeltsch wrote:
(snip)
Related question: Can anybody tell me when there will be Debian packages
of GHC 6.4 available?
See http://packages.debian.org/unstable/devel/ghc6
-- Mark
Okay, I wasn't precise enough
Am Donnerstag, 28. Juli 2005 16:58 schrieb Ian Lynagh:
On Thu, Jul 28, 2005 at 04:37:40PM +0200, Wolfgang Jeltsch wrote:
Related question: Can anybody tell me when there will be Debian packages
of GHC 6.4 available?
There are 6.4 packages in unstable. They aren't installable in unstable
Hello,
I thought, I heard something about a private modules feature in GHC. Was I
just dreaming or is there in fact something like this. I cannot find
information about such a thing.
Best wishes,
Wolfgang
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Hello,
isn't there an option for enabling just generalized deriving for newtypes
without enabling all this other stuff by using -fglasgow-exts?
Best wishes,
Wolfgang
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Glasgow-haskell-users@haskell.org
Hi,
if I enter
ghc -o foo foo.hs
under Windows, is the resulting executable named foo or foo.exe?
(Please send replies not only to the list as I'm not subscribed to it.)
Wolfgang
___
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[EMAIL PROTECTED]
Hello,
I use GHC 5.00.2 on Solaris 2.6 at the university and am unable to use
hierarchical module names --- with and without the -fglasgow-exts switch. GHCi
notifies me of parse errors on the module name. What is interesting is that if
my module with hierarchical name imports a module which
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