At 18:17 18/06/2008, you wrote:
PR Stanley wrote:
>
>
>>PR Stanley wrote:
>> >
>> > [...]
>> >
>> > Paul: I rest my case! :-)
>> > you cowardly hypocrit!
>
> Paul: Why did you remove Jonathan Cast's messa
> PR Stanley wrote:
> > With respect, do you not think it'd be wiser for the community
>
> [snip]
>
> *disgusted*
>
> This is exactly the sort of message that haskell-cafe does not normally
> contain. Let's not start now.
>
> This is a civi
PR Stanley wrote:
>
> [...]
>
> Paul: I rest my case! :-)
> you cowardly hypocrit!
Paul: Why did you remove Jonathan Cast's message? Afraid somebody
might understand why I responded the way I did?
>
Please take your own advice now, and rest your case. Like it or n
anguage sucks rocks" strikes me as unwise.
> >
> >Not necessarily. It can be that they'd implement closures in PHP, make
> >a dog's dinner of it (as they always do), and then we would be blamed
> >for giving them bad advice.
> >
> >Anyway, it seems that P
sarily. It can be that they'd implement closures in PHP, make
a dog's dinner of it (as they always do), and then we would be blamed
for giving them bad advice.
Anyway, it seems that PR Stanley was forced to use PHP, no wonder he's
a little mad at it.
Paul: How did you know? :-)
You
It seems to me that if a PHP developer sees the Haskell community as
a resource for advice on programming language implementation, we
should take this as a compliment to the Haskell community. Repaying
that compliment with "your language sucks rocks"
strikes me as unwise.
I'm familiar w
> Now, if you, Jules, Alex or some other wannabe Hitler have a problem with
> my freedom of expression then your best solution is to saddle up
and get the
> hell out yourselves. This is the wrong place for setting up your tinpot
> dictatorship, Doctor!
Just more evidence...
http://en.wikipe
PR Stanley wrote:
With respect, do you not think it'd be wiser for the community
[snip]
*disgusted*
This is exactly the sort of message that haskell-cafe does not
normally contain. Let's not start now.
This is a civilized mailing list. Either comment on the nice
gentlemen
With respect, do you not think it'd be wiser for the community
[snip]
*disgusted*
This is exactly the sort of message that haskell-cafe does not
normally contain. Let's not start now.
This is a civilized mailing list. Either comment on the nice
gentlemen's PHP closure proposal from a lan
asier simpler faster than the stupid traps.
They are after all /their/ deckchairs to play with.
Yes, playing with deckchairs while the ship sinks with that
bloody woman singing "my Heart Will Go on".
-ljr
PR Stanley wrote:
> Blimey! Talk about rearranging the dec
Blimey! Talk about rearranging the deckchairs :-)
With respect, do you not think it'd be wiser for the community to
deal with a total lack of proper type checking, the lack of any
notion of the general concept of a function, or a whole range of
other fundamental issues in PHP first before worry
Hi
(16 :: Float) is a perfectly legitimate statement although I'm
surprised that it's allowed in a type strong language such as
Haskell. It's a bit like casting in good old C. What's going on here?
Paul
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Hello
Why does sqrt (-16) return NaN? What is NaN?
Thanks
Paul
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Paul: What is the underlying rationale for the Maybe data type?
It is the equivalent of a database field that can be NULL.
Paul: shock, horror! the null value or the absence of any
value denoted by null is not really in harmony with the relational model.
> is it the saf
I don't know Haskell very well, but
Paul: "I'm not racist but . . ." :-)
even I can tell, looking at, for
example, the N-body benchmark, that the Haskell code is probably not
type-safe, and the tricks used in it would not be usable in a larger
program (see below).
The task is esse
Um, I was encountering and recognizing times when I
really needed an
out-of-band "null", and the pain of representing such in C, shortly
after I started serious programming in C (call it 1984-5). Is this
really difficult?
Paul: Hmm, I'm not quite sure what you're driving at.
Paul: Hi folks
data Maybe a = Nothing | Just a
What is the underlying rationale for the Maybe data type?
is it the
safe style of programming it encourages/
Something tells me this is going to start a lengthy discussion. :-)
Bob: Pure and simple -- it allows you to
Paul: Hi folks
data Maybe a = Nothing | Just a
What is the underlying rationale for the Maybe data type?
is it the
safe style of programming it encourages/
Something tells me this is going to start a lengthy discussion. :-)
Bob: Pure and simple -- it allows
Hi folks
data Maybe a = Nothing | Just a
What is the underlying rationale for the Maybe data type? is it the
safe style of programming it encourages/
Something tells me this is going to start a lengthy discussion. :-)
Cheers, Paul
_
Are there any invariants you wish to maintain when inserting? If
not, it's rather trivial.
Paul: The idea is to find a value in the tree greater than
the new value and then placing the new value before it on the tree.
duplicates are ignored and if no value greater than he new value
Actually, you've touched an important point there. It's balancing
that I'm having difficulty with.
Paul
At 23:46 09/05/2008, you wrote:
PR Stanley <[EMAIL PROTECTED]> wrote:
> Hi
> data Ord a => Tree a = Nil | Node (Tree a) a (Tree a)
> How would one go ab
Hi
data Ord a => Tree a = Nil | Node (Tree a) a (Tree a)
How would one go about inserting a value in a binary search tree of
the above description?
Cheers
Paul
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Hi
I thought [1, 2, 3] :: [Int]
GHC says it's (Num t) > [t]
Okay, when it comes to 3.3:[1,2,3] (Num t) => [t] makes more sense.
Is that the only reason?
Cheers,
Paul
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Hi
(take 4 . map (>0)) (f s t)
where
s = 2 : t
t = 3 : s
f = zipWith (-)
What would be the order of evaluation for the above code? How would
I illustrate the evaluation step-by-step?
What do you need it for, really? Pure functional programs are not
about evaluation order, but a
Hi
(take 4 . map (>0)) (f s t)
where
s = 2 : t
t = 3 : s
f = zipWith (-)
What would be the order of evaluation for the above code? How would I
illustrate the evaluation step-by-step?
I'm guessing that the code necessitates lazy evaluation and as such
it starts with take then
Paul: okay, da capo: We prove/test through case analysis
> that the predicate p holds true for the first/starting case/element
> in the sequence. When dealing with natural numbers this could be 0 or
> 1. We try the formula with 0 and if it returns the desired result we
> move onto the next
You've got the right idea.
Paul: At long last! :-)
I should point out that it doesn't make sense to say p(Succ n) =
Succ(p(n)), p(x) represents some statement that is either true or
false, so it doesn't make sense to say Succ(p(n)). .
Paul: okay, da capo: We prove/test through
. If
pn+1) = p(n) + p(1) then we have liftoff!
I'm not going to go any further in case I'm once again on the wrong track.
Cheers
Paul
At 22:43 07/05/2008, you wrote:
On Wed, May 7, 2008 at 9:27 PM, PR Stanley <[EMAIL PROTECTED]> wrote:
> Hi
> One of you chaps mentioned t
Hi
One of you chaps mentioned the Nat data type
data Nat = Zero | Succ Nat
Let's have
add :: Nat -> Nat -> Nat
add Zero n = n
add (Succ m)n = Succ (add m n)
Prove
add m Zero = m
I'm on the verge of giving up on this. :-(
Cheers
Paul
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After you grok induction over the naturals, you can start to think
about structural induction, which is usually what we use in
programming. They are related, and understanding one will help you
understand the other (structural induction actually made more sense to
me when I was learning, because
> Hi
> I don't know what it is that I'm not getting where mathematical
> induction is concerned. This is relevant to Haskell so I wonder if
> any of you gents could explain in unambiguous terms the concept
> please. The wikipedia article offers perhaps the least obfuscated
> definition I've foun
Hi
I don't know what it is that I'm not getting where mathematical
induction is concerned. This is relevant to Haskell so I wonder if
any of you gents could explain in unambiguous terms the concept please.
The wikipedia article offers perhaps the least obfuscated definition
I've found so far bu
Hi
isZero :: Int -> Bool
isZero 0 = True
isZero n | n /= 0 = False
The order in which the above equations appear makes no difference to
the application of isZero. Does the Haskell interpreter rewrite
patterns into one single definition using some sort of switch or if
construct? Why does an equ
Hi
What on earth is unapplying function definitions?
The following is taken from chapter 13 of the Hutton book:
"...when reasoning about programs, function definitions can be both
applied from left to right and unapplied from right to left."
Well, because of referential transparency, we can sa
Hi
What on earth is unapplying function definitions?
The following is taken from chapter 13 of the Hutton book:
"...when reasoning about programs, function definitions can be both
applied from left to right and unapplied from right to left."
Cheers
Paul
Just in case anyone missed this:
[1]
funk f x = f (funk f) x
f :: a
x :: b
funk f x :: c
therefore funk :: a -> b -> c
RHS
f (funk f) x :: c
f (funk f) :: d -> c
x :: d
f :: e -> d -> c
fun
[1]
funk f x = f (funk f) x
f :: a
x :: b
funk f x :: c
therefore funk :: a -> b -> c
RHS
f (funk f) x :: c
f (funk f) :: d -> c
x :: d
f :: e -> d -> c
funk :: h -> e
f :: h
In case you missed it the first time here is my query again:
Hi
I know we've already looked at the topic of function type calculation
though last time I didn't have the chance to go through it
thoroughly. So here it is again. Apologies for the repetition. I've
had a try at calculating function
Hi
I know we've already looked at the topic of function type calculation
though last time I didn't have the chance to go through it
thoroughly. So here it is again. Apologies for the repetition. I've
had a try at calculating function types for two examples below. So to
start with I'd be gratef
What is the difference between
data T0 f a = MkT0 a
instance Eq (T0 f a) where ...
and
data T0 f a = MkT0 a
instance Eq a => Eq (T0 f a) where ...
The second one says that "TO f a" is only an instance of "Eq" if "a"
is, while the first says that "TO f a" is an instanc
Hi
What is the difference between
data T0 f a = MkT0 a
instance Eq (T0 f a) where ...
and
data T0 f a = MkT0 a
instance Eq a => Eq (T0 f a) where ...
I've only seen the "=>" operator used for declaring extended classes
but never with class insta
Hello Hans,
Tuesday, April 8, 2008, 12:17:38 PM, you wrote:
> "deriving" which I think is not used elsewhere. It will break a lot
> of code, but it is easy to change, and also easy to make a
> compatibility mode.
it's also easy to replace all the books, update all code repositories
and reteac
Hi,
Thank you very much for your helpful replies.
So, we define (or is it declare) a class with a polymorphic value(s
which will be used in defining function types or functions associated
with that class. The data types are then used for deriving instances
of that class specific to each data ty
> Hi
> data Bool = False | True
> deriving (Eq, Or, Show, Read)
>
> Bool is an instance of Eq, Ord, Show and Read. It is derived form
> these classes.
No. "deriving ..." here does not mean that Bool is derived from those
classes; it's not a statement about inheritance or anything similar.
"
Hi
data Bool = False | True
deriving (Eq, Or, Show, Read)
Bool is an instance of Eq, Ord, Show and Read. It is derived form
these classes. If that is the meaning of the keyword deriving then
wouldn't a different keyword such as from or derivative or even
derivation be closer to the semantics
Hi
data Bool = False | True
deriving (Eq, Or, Show, Read)
Bool is an instance of Eq, Ord, Show and Read. It is derived form
these classes. If that is the meaning of the keyword deriving then
wouldn't a different keyword such as from or derivative or even
derivation be closer to the semantics
At 12:28 07/04/2008, you wrote:
On Fri, Apr 4, 2008 at 10:49 PM, Andrew Coppin
<[EMAIL PROTECTED]> wrote:
> More to the point, the range y..z goes in steps of y-z. ;-)
[x,y..z] goes in steps of y-x ;-), [y..z] goes in steps of 1
(depending on the type).
Could you elaborate please?
Hi folks
[x, y..z]
What's the role of x?
Cheers,
Paul
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At 14:37 04/04/2008, you wrote:
And how would I cross compile something for that platform with ghc?
(There seems to be no port, which is fine)
Don't look at me mate. :-)
PR Stanley schrieb:
I'm surprised you can't use the Glasgow implementation on CE.
At 13:55
I'm surprised you can't use the Glasgow implementation on CE.
At 13:55 04/04/2008, you wrote:
Is there any Haskell compiler for Windows CE on a XScale platform? I
googled around a bit and found references to a Hugs implementation
but couldn't find any place to download it.
I have the opportuni
Hi folks
> let f = sum.map (^2).filter even
> f [1..4]
20
So far so good!
> sum.map (^2).filter even [1..4]
returns an error.
How is it that the composition above as part of a function equation
doesn't return any errors while on its own it requires parentheses?
You seem to have expression eva
Hi folks
> let f = sum.map (^2).filter even
> f [1..4]
20
So far so good!
> sum.map (^2).filter even [1..4]
returns an error.
How is it that the composition above as part of a function equation
doesn't return any errors while on its own it requires parentheses? I
can understand the need for
Try putting this through your GHCI:
:t twice f x = f (f x)
I'd presume that based on the inference of (f x) f is (t -> t) and x :: t
Yes, Maybe I should get the right associativity rule cleared first.
Cheers,
Paul
At 20:35 01/04/2008, you wrote:
PR Stanley:
I know sort of instinctivel
Are you asking why one doesn't change the rules for all functions? Or
are you asking why Haskell doesn't include a system of user-defined
precedence and associativity for function application so that one could
declare that g binds more tightly than f? I see good reasons for both
questions, but I
Think about this:
map (+1) [1..10]
What should it do?
take (+1) and return a function which takes a list as its
argument and finally return a list.
How about:
f 1 2 3
Should that be f (1 (2 3)), or ((f 1) 2) 3?
The latter, of course, but that's not really what I'm
drivi
HI
It's one of those things - I know sort of instinctively why it is so
but can't think of the formal rationale for it:
f g x = g (g x) :: (t -> t) -> (t -> t)
Why not
(t -> t) -> t -> (t -> t)
to take account of the argument x for g?
Cheers
Paul
___
Hi
If
f x = x
and
g y = y
then
f g x
returns an error because f takes only one argument. Why can't we have
function application implemented outwardly (inside-out). So
f g x would be applied with
gx first followed by its return value passed to f instead of putting
g x in brackets.
Cheers,
Paul
At 13:23 28/02/2008, you wrote:
Hello,
I wish I could be there, but I'm in Kentucky. ;)
It would be great if someone could have this talk recorded and
posted on youtube, or something similar.
Thank you.
Now, there's an idea which could be extended to all Haskell related
gatherings.
__
Actually, I haven't sent this question to the list before. So you're
in no danger of repeating yourself.
Thanks for your kind reply anyway
Paul
At 07:03 17/02/2008, you wrote:
On Feb 17, 2008 6:20 AM, PR Stanley <[EMAIL PROTECTED]> wrote:
> I can't think of an eleg
Hi friends
I'm in the process of designing a series of functions which you might
collectively call a parser. The idea is to evaluate an input string
for a proof software. So a typical input string would be something
like "(P & Q) -> q".
There are a number of things to consider here, for example
Hi
domain, source --- are the two different things? I'm sure I read
somewhere that the source \subseteq domain in mappings. The same was
said about range and target -- target \subseteq range.
Any ideas?
Thanks, Paul
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Hi folks
The disjunction elimination rule:
I've been trying to make sense of it and I think I have had some
success; however, it's far from adequate. I wonder, is there a way of
demonstrating it in Haskell? A code frag with a jargon-free
explanation would be mucho appreciated.
Cheers, Paul
__
I will only consider events where they serve free tea and sandwiches,
plus if there's a landing pad for the chopper nearby. :-)
At 23:11 07/02/2008, you wrote:
The community might be interested to know that there are (at least)
7 Haskell/FP user groups meeting across the world in the next two
Thanks, keep the tips coming. I like the ones about the type safety
and line counts.
Cheers,
Paul
At 23:33 04/02/2008, you wrote:
Good luck with this - I'd love to see the outcome.
My experience is that FP tends to result in a lot less code, so if
there are x
bugs per line of code, FP has les
Hi folks
I'm thinking of writing a little essay arguing the case for the
advantages of FP for producing quality software. Can the list
recommend any papers/articles which I can use as sources of my
argument? I have access to the IEEE database too although earlier I
couldn't find anything on th
At 16:16 29/01/2008, you wrote:
Am Dienstag, 29. Januar 2008 02:25 schrieb Tim Chevalier:
> On 1/28/08, [EMAIL PROTECTED]
>
> <[EMAIL PROTECTED]> wrote:
> > Well, unless you are French. Then you don't pronounce "H". The remaining
> > letters are pronounced according to the Règlements de l'Acadé
Hi
What does the list think of EC? Genetic algorithm is apparently the
latest thing.
Is EC mathematically reasonable?
Paul
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Hi
Can the list recommend books that use Haskell - or any FP language
but preferably Haskell - to illustrate the principles of compilers
and/or algorithms?
I think most of you would understand if I said that I'd prefer FP
code instead of funny math symbols that don't translate into ANSI
chara
Hi
According to the Haskell Wikibook the is the
opposite of $. The text also oints out that the
"|>" can be used as a substitute. I tried using
|> but to no avail. Is the list au fait with the |> operator?
Thanks,
Paul
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Hi
I've probably asked about the do construct, if that's the right
label. Unfortunately I'm still not quite sure of its role and more
specifically its syntax. Something to do with generators perhaps? A
description plus some examples would be most gratefully received.
Thanks, Paul
Hi
Does the list consider
http://en.wikibooks.org/w/index.php?title=Haskell/Understanding_monads&oldid=933545
a reliable tutorial on monads and, if not, could you recommend an
onlien alternative please?
Thanks,
Paul
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Haske
That's a very good point. Yes, let's have some detailed explanations
accompanied by some good examples.
Cheers, Paul
At 08:43 03/12/2007, you wrote:
> I agree that (in this context, beginning learning Haskell) it is a
> somewhat minor issue. But I disagree that this is something you should
> ig
Hi
data Tree = Leaf Int | Node Tree Int Tree
occurs :: Int -> Tree -> Bool
occurs m (Leaf n) = m == n
occurs m (Node l n r) = m == n || occurs m l || occurs m r
It works but I'd like to know if it can be improved in any way.
Thanks, Paul
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Hi
> type assoc k v = [(k, v)]
works beautifully and everything makes sense.
> type Assoc v = (Ord k) => [(k, v)]
This doesn't work. Is there any wayof defining k as an element of
type Ordinal. I could redefine k by putting Char or Int in its place.
Why can't I be more general?
Thanks,
Paul
> PRS: (>>=) :: Parser a -> Parser b -> Parser b
> p >>= f = \inp ->
>case p inp of
> [] -> []
> [(v, out)] -> parse (f v) out
You probably want:
(>>=) :: Parser a -> (a -> Parser b) -> Parser b
p >>= f = \inp -> case parse p inp of
[] -> []
Hi
(>>=) :: Parser a -> Parser b -> Parser b
p >>= f = \inp ->
case p inp of
[] -> []
[(v, out)] -> parse (f v) out
based on a lot of guesswork, after the mess created by the OCR, I
managed to get the above example to work syntactically but is it
semantically correct?
Thanks, Paul
__
Hi
taken from ch.8.3 in the Hutton book:
"Whereas return v always succeeds, the dual parser failure always
fails regardless of the contents of the input string:"
The dual parser failure?
Cheers,
Paul
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Hi
Thanks for the response.
JCC: In most languages, if you have some expression E, and when the
computer attempts to evaluate E it goes in to an infinite loop, then
when the computer attempts to evaluate the expression f(E), it also
goes into an infinite loop, regardless of what f is. That's
Hi
Thanks for the explanation. I would be grateful for some examples
accompanying the text. I will indicate the right places for real life
(Haskell code) examples in the paragraphs below:
PJ: As I understand it, the distinction is between the mathematical
term "non-strict" and the implementa
also, Latex source code is 100% accessible to screen reader users.
Paul
You are completely right, 99% of the people will read the PDF, in
exactly the same sense that Windows users prefer to download an
installable EXE instead of building from source.
But nobody here will argue that the *opti
Hi Peter,
> Yes, but why don't researchers just publish their TEX file? You can
> regard that as the "source code" for generating PDF/PS whatever no?
Building a .tex file can be rather hard with packages and what-not,
plus quite a few of us use lhst2tex as a preprocessor. It's not
impossible,
Why don't you typeset the whole thing in Latex. That way you'll
definitely ensure accessibility.
Cheers
Paul
At 19:43 19/11/2007, you wrote:
Most research papers have the same layout: two columns per A4 page.
They mostly come as PDF or PS.
Although this is standard, it is not really accessible
Hi
okay, so $! is a bit like $ i.e. the equivalent of putting
parentheses around the righthand expression. I'm still not sure of
the difference between $ and $!. Maybe it's because I don't
understand the meaning of "strict application". While we're on the
subject, what's meant by Haskell being
Hi
I understand 2%4 will construct a fraction in Haskell. I've tried
this in GHCI but got an error message. Is there such an operator in
Prelude and if so how is it applied?
Cheers,
Paul
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http://w
ed in the idea of a straightahead MS Windows GUI for
my program but dont' really know where to start.
Any advice would be most appreciated.
Cheers
Paul
At 17:13 12/11/2007, you wrote:
On Nov 12, 2007, at 8:38 AM, PR Stanley wrote:
Hi
back again!
How easy/hard is it to control a haske
Hi
What is the role of $! ?
As far as I can gather it's something to do with strict application.
Could someone explain what it is meant by the term strict application please?
Thanks,
Paul
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> Hi brazilian haskellers,
Wow! I knew the Haskell community has been growing... but there's a
brazillian of us?
--
Rich
A mini UN, that's us.
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Hi
back again!
How easy/hard is it to control a haskell program through a web browser?
Cheers
Paul
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Hi folks
Apologies for the off-topic post.
If anyone knows anything about the rules of proof by deduction and
quantifiers I'd be grateful for some assistance.
Much obliged,
Paul
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f x = x
x :: a
f x :: b
therefore f :: a -> b
x = a and x = b
therefore a = b
therefore f :: a -> a
Simple mappings are easy to work out. It's the more detailed stuff
I'm not sure about.
f g x y = g x (y x)
Cheers, Paul
At 03:15 23/10/2007, you wrote:
On 10/22/07, PR Stanley
Hi
What are the rules for calculating function types?
Is there a set procedure ?
Thanks, Paul
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Hi
data Bin = Zero | One
As suggested by someone on this list. It's a really neat idea
although I'm wondering how I can apply this to my int to binary
function. The Zero or One declaration is saying that Bin is a data
type that can hold either a one or a zero. I tried testing this with
a
At 01:48 19/10/2007, you wrote:
On Fri, Oct 19, 2007 at 02:45:45AM +0200,
[EMAIL PROTECTED] wrote:
> PR Stanley writes:
>> One of the reasons I'm interested in Wikipedia and Wikibook is because
>> you're more likely to find Latex source code used for typesetting the
Hi
thank you for all your replies.
One of the reasons I'm interested in Wikipedia and Wikibook is
because you're more likely to find Latex source code used for
typesetting the maths.
Latex is the one and only 100% tool right now.
A lot of publishers use Latex but try to get anything from them i
Hi
Do you trust mathematical materials on Wikipedia?
Paul
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Hi
is const = id?
const 'x' 'y'
'x'
id 'x'
'x'
Cheers,
Paul
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Thanks for the very clear explanation. More questions:
What is the role of ">>"?
How is ">>" different to ">>="? I am aware that ">>=" is used for
sequencing parsers but that's all I know about it.
Thanks, Paul
At 22:28 13/1
Hi
"do", what's its role?
I know a few uses for it but can't quite understand the semantics -
e.g. do putStrLn "bla bla"
So, what does do, do?
Thanks, Paul
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Hi
I'm reading the chapter on parsers in the Hutton book. The text
refers to the data type tree which doesn't seem to be in prelude. So,
I was wondering, what would be asuitable tree for a parser? A binary
tree perhaps? Are there different types of tree for different parsers?
Thanks,
Paul
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Hi
failure :: (Parser a) failure = \inp -> []
The code might contain some syntax errors and I'd be grateful for any
corrections.
What is a "dual parser failure"?
Thanks,
Paul
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