Rewriting Char.ord

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Rewriting char

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agda v. haskell

PR Stanley

29 Sep 2007 29 Sep '07

2:11 p.m.

Hi ord :: Char -> Int ord c = sum [1 | x <- ['\0'..'\255'], x < c] Any comments? Any alternatives? Cheers, Paul

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Felipe Almeida Lessa

29 Sep 29 Sep

2:23 p.m.

(sending the e-mail again, this time with CC to the list) On 9/29/07, PR Stanley wrote:

...

Hi ord :: Char -> Int ord c = sum [1 | x <- ['\0'..'\255'], x < c]

Any comments? Any alternatives?

Well, you're using Enum class there, so maybe you want ord' = fromEnum Also, an alternative is to stop the loop as soon as possible ord'' c = length $ takeWhile (< c) ['\0'..'\255'] Humm... and it seems that you can have Char's above '\255', so it would be wiser to use ord''' c = length $ takeWhile (< c) ['\0'..] -- Felipe.

Stefan O'Rear

2:26 p.m.

On Sat, Sep 29, 2007 at 03:11:20PM +0100, PR Stanley wrote:

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Hi ord :: Char -> Int ord c = sum [1 | x <- ['\0'..'\255'], x < c]

Any comments? Any alternatives? Cheers, Paul

It's waay slow, it breaks for characters >255. ord :: Char -> Int ord = fromEnum As Char is an instance of 'Enum'. If you think this is cheating, then consider that (<) for Char is probably implemented using ord on some level. You need primitives somewhere... Stefan

PR Stanley

2:37 p.m.

Okay, a couple of things what is fromEnum? What's the role of % in length 5 takeWhile (

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On Sat, Sep 29, 2007 at 03:11:20PM +0100, PR Stanley wrote:

...
Hi ord :: Char -> Int ord c = sum [1 | x <- ['\0'..'\255'], x < c]

Any comments? Any alternatives? Cheers, Paul

It's waay slow, it breaks for characters >255.

ord :: Char -> Int ord = fromEnum

As Char is an instance of 'Enum'.

If you think this is cheating, then consider that (<) for Char is probably implemented using ord on some level. You need primitives somewhere...

Stefan

Antoine Latter

3:19 p.m.

(sending to the whole list this time ...) On 9/29/07, PR Stanley wrote:

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Okay, a couple of things what is fromEnum?

fromEnum :: (Enum a) => a -> Int fromEnum 'c' :: Int 'fromEnum' converts any member of the "Enum" typeclass to an 'Int'. It works fine for a Char.

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What's the role of % in length 5 takeWhile (

I assume you mean the '$': ($) :: (a -> b) -> a -> b It's the function application operator, but it has extremely low precedence, so it applies everything to it's left to everything to its right. It's mainly a tool for cutting down on writing paranthesis: f (1 + 1) = f $ 1 + 1

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Antoine Latter
Felipe Almeida Lessa
PR Stanley
Stefan O'Rear