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Today's Topics:
1. Empty or Tree? (bahad?r altan)
2. Parsec, parsing 'free text' (Franco)
3. Re: Empty or Tree? (Aditya Manthramurthy)
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Message: 1
Date: Sat, 10 Mar 2012 10:28:43 +0000 (GMT)
From: bahad?r altan <[email protected]>
Subject: [Haskell-beginners] Empty or Tree?
To: "[email protected]" <[email protected]>
Message-ID:
<[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Hello everyone. I'm trying to write a code which works on binary trees. When I
write code like this ?with a tree with empty nodes :
data Tree ?= ?Empty | Node ?Integer Tree Tree
function Node a (Node b Empty Empty)??(Node c Empty Empty)
it works fine.?
But when I try to create a more generic code like this ?which could ?work with
trees who don't have empty nodes in grandchild level :?
function Node a (Node b Tree Tree)??(Node c Tree Tree )?
I get this error :?Undefined data constructor "Tree"
Can you help me with creating more generic code please?
Thanks
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Message: 2
Date: Sat, 10 Mar 2012 11:49:24 +0100
From: Franco <[email protected]>
Subject: [Haskell-beginners] Parsec, parsing 'free text'
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII
I am using Parsec as my parsing library and quite liking it: though, I am
unsure on how to properly tackle a 'free element' problem. Let me explain:
In my file, there are some elements which look like this:
this is some <red - formatted> text.
I call this a FormatString. They can be found inside many elements, like:
[ someconditions | this is some <red - formatted> text.]
+ this is some <red - formatted> text. -> somenumberhere
To parse a FormatString I call 'generalText', which looks like this:
56 -- TEXT --
57
58 generalText = many anyText >>= \fss ->
59 return (foldl (+:+%) (toFString "" []) fss)
60
61 anyText = try ( formattedText )
62 <|> plainText
63
64 formattedText = char '<' >>
65 sepEndBy1 format spacebar >>= \fs -> -- format parser
66 string "- " >>
67 manyTill anyChar (char '>') >>= \cs ->
68 return (toFString cs fs)
69
70 plainText = many1 (noneOf "<") >>= \xs ->
71 return (toFString xs [])
It works, but causes quite some headaches in using it:
- I would like to call a "read with generalText until you find a ']'
character.
- or a "read with generalText until you find a " -> " (do not consume
it)
And the like, but I do not know how. If it were a plain string I would call
manyTill1 anyChar myP. I thought of first parsing a raw string searching for a
terminator and then feeding it to generalText. But isn't that cluncky codewise?
Thanks for your help
-F
------------------------------
Message: 3
Date: Sat, 10 Mar 2012 16:27:50 +0530
From: Aditya Manthramurthy <[email protected]>
Subject: Re: [Haskell-beginners] Empty or Tree?
To: [email protected]
Message-ID:
<cac_me97dzmbvg3rtnava4qv1vanpdhnt97cg+ercsk2dgtn...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
I think this is because "Tree" is a data type and not a data constructor.
According to your definition of Tree, Empty and Node are the constructors.
Node a (Node b (Node c Empty Empty) (Node d Empty Empty)) (Node e (Node f
Empty Empty) (Node g Empty Empty))
is a valid tree if a, b, c, d, e, f, g are integers.
Hope this helps.
--
Aditya.
On 10 March 2012 15:58, bahad?r altan <[email protected]> wrote:
> Hello everyone. I'm trying to write a code which works on binary trees.
> When I write code like this with a tree with empty nodes :
>
> data Tree = Empty | Node Integer Tree Tree
>
> function Node a (Node b Empty Empty) (Node c Empty Empty)
>
> it works fine.
> But when I try to create a more generic code like this which could work
> with trees who don't have empty nodes in grandchild level :
>
> function Node a (Node b Tree Tree) (Node c Tree Tree )
>
> I get this error : Undefined data constructor "Tree"
>
> Can you help me with creating more generic code please?
> Thanks
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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