Hello!
probably it's me, but I cannot understand what I'm doing wrong.
I'm trying to learn HaXml. I've never used it before and I never did
xml processing in Haskell. So I'm a total newbie!!
I downloaded and compiled. Everything seems fine. I'm also able to run
some examples in the related
Il Sat, Sep 09, 2006 at 09:58:03AM -0700, Jason Dagit ebbe a scrivere:
Maybe ...use -package HaXml interactively with GHCi... (That's from
the HaXml website.)
I'm using -package HaXml, obviously, otherwise the module would not
load.
What I do not understand is that unresolved symbol message: I
Il Fri, Sep 01, 2006 at 10:43:14AM +0400, Bulat Ziganshin ebbe a scrivere:
imho, your tutorial makes the error that is a very typical: when you
write your tutorial you already know what are monads and what the
program you will construct at the end. but your reader don't know all these!
Ok, so
Il Sun, Sep 03, 2006 at 12:26:25AM +0200, Tomasz Zielonka ebbe a scrivere:
On Sat, Sep 02, 2006 at 09:51:26PM +0200, Benjamin Franksen wrote:
However, in order to 'run' (i.e. finally actually use) a monadic value
that involves an application of bind, the latter would have to supply
some
Il Fri, Sep 01, 2006 at 07:22:02AM +0200, Tomasz Zielonka ebbe a scrivere:
On Fri, Sep 01, 2006 at 01:13:14AM +0200, Benjamin Franksen wrote:
So getting the value out of the monad is not a pure function (extract ::
Monad m = m a - a). I think I stated that, already, in my previous post.
Il Fri, Sep 01, 2006 at 10:43:14AM +0400, Bulat Ziganshin ebbe a scrivere:
The tutorial will have this outline: first we build a monad adding
output, exception, and state. Then we use monad transformer to take
out state and output and add debug, doing lifting, put(ing) and
get(ing) by
Il Wed, Aug 30, 2006 at 11:24:45AM +0100, Brian Hulley ebbe a scrivere:
Thanks, glad to be of help.
I met Haskell a couple of months ago, when I switched my window
manager to Ion. Tuomo Valkonen, its developer, uses darcs. Moreover he
develops a small PIM, riot, written in Haskell. I wanted to
Il Thu, Aug 31, 2006 at 02:39:59PM +0100, Simon Peyton-Jones ebbe a scrivere:
Andrea
Don't forget to link to it from here!
http://haskell.org/haskellwiki/Books_and_tutorials#Using_monads
Simon,
I'll do. But now the text is far from being complete: there's only the
code... (the most
Il Thu, Aug 31, 2006 at 07:23:55PM +0200, Benjamin Franksen ebbe a scrivere:
I argued that monadic values get 'chained' in a very specific way and that
in order to get an intuition about what this monadic chaining really means
on the most general level, the standard model of 'computation that
Il Tue, Aug 29, 2006 at 10:02:38AM +0100, Brian Hulley ebbe a scrivere:
Hi!
Ím getting back so late because it took me a while to understand
monadic transformation...
data Result a
= Good a State Output
| Bad State Output
deriving Show
...
case runSOIE m x of
Il Tue, Aug 29, 2006 at 07:45:46AM +0100, Brian Hulley ebbe a scrivere:
Andrea Rossato wrote:
Il Mon, Aug 28, 2006 at 09:28:02PM +0100, Brian Hulley ebbe a
scrivere:
where the 4th element of the tuple is True iff we can continue or
False iff an exception occurred.
I'm starting to believe
Il Tue, Aug 29, 2006 at 10:02:38AM +0100, Brian Hulley ebbe a scrivere:
Yes I agree the StateT/monad transformer approach is probably best in the
long run, since by using the standard monad transformers, you will get code
that will scale better to handle more complexities later, and has the
Hello!
Sorry if I keep bothering, but I'm still trying to understand types and
monads.
Now I'm trying to create a statefull evaluator, with output and
exception, but I'm facing a problem I seem not to be able to
conceptually solve.
Take the code below.
Now, in order to get it run (and try to
Il Mon, Aug 28, 2006 at 08:23:15PM +0200, Andrea Rossato ebbe a scrivere:
The previous code was not complete, and so testable.
at the end there is the output.
there it is:
module Monads where
data Term = Con Int
| Add Term Term
deriving (Show)
type State = Int
type Output
Il Mon, Aug 28, 2006 at 09:28:02PM +0100, Brian Hulley ebbe a scrivere:
data Eval_SOI a = SOIE {runSOIE :: State - (a, State, Output, Bool)}
seems simple and neat...
else r1
ie if runSOIE m x does not result in an exception then we continue with the
second computation otherwise
Il Mon, Aug 28, 2006 at 09:28:02PM +0100, Brian Hulley ebbe a scrivere:
where the 4th element of the tuple is True iff we can continue or False iff
an exception occurred.
I'm starting to believe that the best method is just take the way
StateT takes... without reinventing the wheel...
Il Sat, Aug 26, 2006 at 02:02:36AM +0200, Andrea Rossato ebbe a scrivere:
perhaps this is silly, but it is not possible to declare function
types?
could you please indicate me some documentation that explains this
kind of stuff? So far I didn't find anything on that.
well, I've found
Il Sat, Aug 26, 2006 at 11:55:34AM +0100, Brian Hulley ebbe a scrivere:
Yes, it's useful because it allows you to make a distinction between
different uses of the same type of function and make these different uses
into instances of different classes. It also allows you to hide the fact
Il Sat, Aug 26, 2006 at 06:00:02PM +0400, Bulat Ziganshin ebbe a scrivere:
type HashFunction = (String-Int)
...
createHash :: HashFunction - IO Hash
and
createHash :: (String-Int) - IO Hash
are equivalent. So, technically speaking, you can't declare function
types, there is only one
Il Fri, Aug 25, 2006 at 01:13:58PM -0400, Cale Gibbard ebbe a scrivere:
Hey cool, a new monad tutorial! :)
Just out of interest, have you seen my Monads as Containers article?
http://www.haskell.org/haskellwiki/Monads_as_Containers
Let me know what you think of it. I find that often
Il Thu, Aug 24, 2006 at 08:02:38PM +0100, Neil Mitchell ebbe a scrivere:
Just shove it on the wiki regardless. If its useless then no one will
read it. If its a bit unreadable, then people will fix it. If its
useful the world will benefit. Any outcome is a good outcome!
Ok: I've put it on the
Hello!
I cannot understand this piece of code:
type Z = Int
type T a = Z - (a, Z)
Il Fri, Aug 25, 2006 at 07:52:35PM +0100, Neil Mitchell ebbe a scrivere:
why mkT is a type constructor and mkT1 seems not to be?
In what way is mkT a type constructor? In this program only T1 is a
type constructor, as far as I can see.
read my sentence as
why T is a type constructor and T1
Il Fri, Aug 25, 2006 at 08:35:01PM +0100, Brian Hulley ebbe a scrivere:
It is maybe easier to just think of a newtype decl as being the same as a
data decl except for the fact that you can only have one constructor on the
rhs whereas a data decl allows multiple constructors, and a type decl
Il Sat, Aug 26, 2006 at 01:27:38AM +0200, Daniel Fischer ebbe a scrivere:
Because T a is a function type, namely Int - (a,Int), so
...
iHowever, neither T1 a nor T2 a is a function type, a value of type
T1 a is a function _wrapped by the data (or value) constructor T1_ (the same
applies to
Il Sat, Aug 26, 2006 at 01:27:38AM +0200, Daniel Fischer ebbe a scrivere:
unT1 :: T1 a - T a
unT1 (T1 f) = f
makeT1 a b = unT1 (mkT1 a) b
will work fine.
*Prelude :t makeT1
makeT1 :: a - Int - (a, Int)
*Prelude
not that fine, though. Quite useless.
try chancing to:
unT1 :: T1 a - T1
`
mkMO a
evalMO (Add t u) = evalMO t `bindMO` \a -
evalMO u `bindMO` \b -
outMO (formatLine (Add t u) (a + b)) `combineMO`
mkMO (a + b)
That's it. For today...
(TO BE CONTINUED)
Andrea Rossato
arossato
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