HI && TypeCast

[Iavor Diatchki]

hello,

Fredrik Petersson wrote:
> Hi there!
> Iam new to the list so feel free to shout at me when i do wrong! :)
> Software-designer from sweden, likes fast bikes and metal, thats me, and hi
> to you all!
welcome

> Yeah ok to the problem,
> i have this stupid code,
> [c | (c,i) <- l]
> 
> Where (c,i) are a tuple from a (Char,Int) and l is a [(Char,Int)]
> So far everthings nice but i would like to cast the c to a Sting and add :
> in front,
> So if i fry with a list like [('d',3)('f',3)]
> I end up with
> "fg" but i want it to look like
> ":f :g"
> 
> piece of cake, huh?
> Give me a hit or a webpage to read more from...?
> How do you TypeCast in haskell?
no type casting in haskell.  and we think of that as a feature, not a 
bug :-)

having said that, you can write functions that convert values of one 
type into values of another.  for example:
toString :: Char -> String
toString c = [c]

in Haskell the type String is the same as [Char], i.e. a string is a 
list of characters.

another useful predefined function is:
concat :: [[a]] -> [a]
that given a list of lists will produce a "flattened" list that contains 
all the elements, e.g. concat [[1,2],[3,4]] = [1,2,3,4].

in particular when you take 'a' above to be Char you get:
concat :: [String] -> String
which takes a list of strings and gives you back a single string 
containing all the input strings.

now you can achieve what you wanted as:
concat [ ":" ++ toString c ++ " " | (c,i) <- l ]

++ joins two lists into a single list.  there are a lot of useful 
functions in the Prelude.

hope this helped.  by the way a better list to post questions when you 
are stuck with a program is probably haskell-cafe@haskell.org, but 
people will usually reply on either list.

bye
iavor



-- 
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| Iavor S. Diatchki, Ph.D. student               |
| Department of Computer Science and Engineering |
| School of OGI at OHSU                          |
| http://www.cse.ogi.edu/~diatchki               |
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