Hi all, I am an Haskell newbie; can someone explain me why there is
no reported error in @legSome@ but there is one in @legSomeb@
(I used leksah as an IDE, and my compiler is:
$ ghc -v
Glasgow Haskell Compiler, Version 7.2.1, stage 2 booted by GHC version
6.12.3 )
What I do not understand is
Perhaps you should give us the error the compiler give you.
Plus:
data LegGram nt t s = Ord nt = LegGram (M.Map nt [RRule nt t s])
will become invalid. Currently, such class constraints are ignored.
You should remove the 'Ord nt' constraint and add it to you legSome
function. (Maybe that's a
On Tue, Jan 3, 2012 at 5:43 PM, AUGER Cédric sedri...@gmail.com wrote:
legSomeb :: LegGram nt t s - nt - Either String ([t], s)
-- but without it I have an error reported
legSomeb (LegGram g) ntV =
case M.lookup ntV g of
Nothing - Left No word accepted!
Just l - let sg = legSomeb
On Tue, Jan 3, 2012 at 05:17, Yucheng Zhang yczhan...@gmail.com wrote:
subsome :: [RRule nt t s] - Either String ([t], s)
It seems to me that the compiler is not sure the two 'nt' are equal.
The ScopedTypeVariables can make the compiler believe they are equal.
But ScopedTypeVariables is
On Tue, Jan 3, 2012 at 6:44 PM, Brandon Allbery allber...@gmail.com wrote:
On Tue, Jan 3, 2012 at 05:17, Yucheng Zhang yczhan...@gmail.com wrote:
subsome :: [RRule nt t s] - Either String ([t], s)
It seems to me that the compiler is not sure the two 'nt' are equal.
The ScopedTypeVariables
On Tue, Jan 3, 2012 at 05:50, Yucheng Zhang yczhan...@gmail.com wrote:
On Tue, Jan 3, 2012 at 6:44 PM, Brandon Allbery allber...@gmail.com
wrote:
On Tue, Jan 3, 2012 at 05:17, Yucheng Zhang yczhan...@gmail.com wrote:
subsome :: [RRule nt t s] - Either String ([t], s)
It seems to me
As I understand it, both ways work.
legSome ((LegGram g)::LegGram nt t s) ntV
If you compile this without ScopedTypeVariables extension, GHC will
remind you of it:
Illegal signature in pattern: LegGram nt t s
Use -XScopedTypeVariables to permit it
So another solution is to avoid
That is error-prone.
Plus the code does not need ScopedTypeVariables. The real problem comes
from the use of a class constraint on the LegGram data constructor.
data LegGram nt t s = Ord nt = LegGram (M.Map nt [RRule nt t s])
Short answer: you *can't *add class constraints to an already declared
On Tue, Jan 3, 2012 at 06:35, Yucheng Zhang yczhan...@gmail.com wrote:
legSome ((LegGram g)::LegGram nt t s) ntV
If you compile this without ScopedTypeVariables extension, GHC will
remind you of it:
Illegal signature in pattern: LegGram nt t s
Use -XScopedTypeVariables to
On Tue, Jan 3, 2012 at 7:46 PM, Brandon Allbery allber...@gmail.com wrote:
Right, but I think this is conflating two aspects of ScopedTypeVariables and
may not bring them into scope fully. Although, that's a question for
someone who understands ghc's type system far better than I do.
I found
On Tue, Jan 3, 2012 at 06:43, Yves Parès limestr...@gmail.com wrote:
That is error-prone.
Plus the code does not need ScopedTypeVariables. The real problem comes
from the use of a class constraint on the LegGram data constructor.
data LegGram nt t s = Ord nt = LegGram (M.Map nt [RRule nt t
On Tue, Jan 3, 2012 at 7:49 PM, Yucheng Zhang yczhan...@gmail.com wrote:
I found some descriptions of ScopedTypeVariables here:
http://hackage.haskell.org/trac/haskell-prime/wiki/ScopedTypeVariables
Sorry, I found just now a more up-to-date description in the GHC documentation:
Thanks all,
I finally give up to put Ord in the LegGram type.
What was annoying me was that @legsome@ was in fact an instance of a
class I defined. So I changed its signature to make it depend on Ord.
That is not very nice, since at first glance, there could be
implementations which does not
The other much simpler solution no one has mentioned yet is to just
pull 'subsome' out as its own top-level declaration. Having such a
big function nested locally within a 'let' is ugly anyway, and it
makes it harder to test and debug than necessary.
-Brent
On Tue, Jan 03, 2012 at 05:44:01PM
On Wed, Jan 4, 2012 at 12:44 AM, Yves Parès limestr...@gmail.com wrote:
Remove subsome type signature. You are redeclaring type variables which
obviously cannot match those of legSome.
This cannot work without scoped type variables (and ad-hoc foralls to bring
them to scope, of course).
That
Brent is right. Separating functions is nicer to read and cleaner. Plus it
enhances testability.
I wonder why the redeclared type variables cannot match those of legSome?
Try to put a totally wrong type to subsome, like
subsome :: Int
and tell us from the error what type is actually inferred.
On Wed, Jan 4, 2012 at 1:07 AM, Yves Parès limestr...@gmail.com wrote:
Try to put a totally wrong type to subsome, like
subsome :: Int
and tell us from the error what type is actually inferred.
The error is like
Couldn't match type `nt' with `Int'
`nt' is a rigid type variable bound
On Wed, Jan 4, 2012 at 1:38 AM, Yucheng Zhang yczhan...@gmail.com wrote:
On Wed, Jan 4, 2012 at 1:07 AM, Yves Parès limestr...@gmail.com wrote:
Try to put a totally wrong type to subsome, like
subsome :: Int
and tell us from the error what type is actually inferred.
Sorry, I found I
On Wed, Jan 4, 2012 at 1:07 AM, Yves Parès limestr...@gmail.com wrote:
I wonder why the redeclared type variables cannot match those of legSome?
Try to put a totally wrong type to subsome, like
subsome :: Int
and tell us from the error what type is actually inferred.
The actually inferred
2012/1/3 Yucheng Zhangyczhan...@gmail.com
(Hopefully being a little more explicit about this can help you
understand where things are going wrong.)
[--snip--]
legSome :: LegGram nt t s - nt - Either String ([t], s)
The 'nt' you see above
legSome (LegGram g) ntV =
case Main.lookup
On Wed, Jan 4, 2012 at 2:48 AM, Bardur Arantsson s...@scientician.net wrote:
'subsome' to a different type than the one you intended -- and indeed one
which can't be unified with the inferred type. (Unless you use
ScopedTypeVariables.)
Thanks for the reply.
Actually, my question is why the
Hi all,
No Haddock documentation seems to have been generated on Hackage in the
past few days. See e.g.
http://hackage.haskell.org/package/copilot-2.0.3
or http://hackage.haskell.org/package/derive-2.5.5
Does anyone know if the cron job (or whatever) isn't running for some
reason?
Jan Christiansen wrote:
On Jan 2, 2012, at 2:34 PM, Heinrich Apfelmus wrote:
Without an explicit guarantee that the function is incremental, we can't do
anything here. But we can just add another constructor to that effect if we
turn ListTo into a GADT:
data ListTo a b where
On Tue, Jan 03, 2012 at 07:14:58PM +, Bardur Arantsson wrote:
No Haddock documentation seems to have been generated on Hackage in the
past few days.
The machine's down, I think. I'll give it a kick tomorrow.
___
Haskell-Cafe mailing list
Hi Ryan,
Ryan Grant [mailto:rgr...@rgrant.org] said:
Are packages cabal-installed using --global?
The packages that come with a compiler or Haskell Platform are installed
--global. Every other package is installed with cabal, by default into the
user's space.
Is it mostly reliant on cabal or
Actually, my question is why the different type can't be unified with the
inferred type?
Because without ScopedTypeVariable, both types got expanded to :
legSome :: *forall nt* t s. LegGram nt t s - nt - Either String ([t], s)
subsome :: *forall nt* t s. [RRule nt t s] - Either String ([t],
If you're interested in learning parsec, RWH covered this topic in depth in
Chapter 16, Choices and Errors:
http://book.realworldhaskell.org/read/using-parsec.html.
On Mon, Jan 2, 2012 at 3:44 AM, max m...@mtw.ru wrote:
I want to write a function whose behavior is as follows:
foo
I am getting the compilation error below when building GHC 7.0.4 on RHEL5
(x86_64) – I configured make to point to ncurses and libgmp. I will appreciated
pointers on how to work around the issue below. I don’t have root privileges.
My apologies if this has already been discussed in this
My apologies for posting it here. Glasgow-haskell-users mailing list seems
more relevant for this question. So, I am going to send it there instead,
with a note about this cross-posting.
On Tue, Jan 3, 2012 at 4:26 PM, Sanket Agrawal sanket.agra...@gmail.comwrote:
I am getting the compilation
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