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Today's Topics:
1. Pound character use in code? (M.v.Gulik)
----------------------------------------------------------------------
Message: 1
Date: Tue, 23 Oct 2012 10:31:56 +0200
From: "M.v.Gulik" <[email protected]>
Subject: [Haskell-beginners] Pound character use in code?
To: "[email protected]" <[email protected]>
Message-ID:
<caospiufcnsvvhtdeqttbqmvgbn9ecnpjwyzh9famvfczb02...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi
Trying to learn a bit about Haskell as general (script) coder (batch,
autoit, python).
And run into some code I don't get. (could not find the right online
doc that explained it.)
[Code]
length' :: [a] -> Int
length' l = len l 0#
where
len :: [a] -> Int# -> Int
len [] a# = I# a#
len (_:xs) a# = len xs (a# +# 1#)
[/Code]
source:
http://www.haskell.org/ghc/docs/latest/html/libraries/base/src/GHC-List.html#length
1) What is the purpose of the used pound/"#" character here. (Looks
like some type-casting, but that's just a wild guess from me here.
(I'm not a C~ or Java coder))
2) kinda the same for the "I#" in the "len [] ..." line. As the length
function takes only one return result. (note: its a capital i and not
a lowercase L.)
3) Why is it giving a compile error on the "where" line. Error:
"Haskell\baby.hs:<lineNr>:9: parse error on input `where'" (while the
adjusted code below compiles fine. Tab(4s) indented.)
[Code]
length' :: [a] -> Int
length' l = len l 0
where
len :: [a] -> Int -> Int
len [] a = a
len (_:xs) a = len xs (a + 1)
[/Code]
Using: WinGHCi 1.0.6 on Windows Xp. (Haskell Platform 2012.2.0.0
windows install)
TIA
MvGulik
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