On Apr 12, 2009, at 11:50 PM, michael rice wrote:
I'm not sure what you're trying to tell me, so let's try a specific
case.
Here's the makeVerifier function that expects its function f to have
a single arg, a pair (i,d):
makeVerifier :: ((Int,Int) -> Int) -> Int -> (Int -> Bool)
makeVerifier f m = divides m . foldl (+) 0 . map f . zip [1 .. ] .
digits
And usage:
let checkCc = makeVerifier (\ (i d) -> if odd i then d else if d < 5
then 2*d else 2*d + 1) 10
This looks like it has a typo -- did you mean \ (i, d) -> rather than
\ (i d) -> ?
And here's the old makeVerifier function that expects its function f
to have two integer arguments, i & d:
makeVerifier :: (Int -> Int -> Int) -> Int -> (Int -> Bool)
makeVerifier f m = divides m . foldl (+) 0 . zipWith f [1 .. ] .
digits
And usage:
let checkCc = makeVerifier (\ .... <== Complete this ) 10
let checkCc = makeVerifier (\ i d -> if odd i then d else if d < 5
then 2*d else 2*d + 1) 10
though I find it a bit nicer to expand it a bit for clarity:
checkCc :: Int -> Bool
checkCc = makeVerifier f 10
where
f i d | odd i = d
| d < 5 = 2*d
| otherwise = 2*d + 1
-Ross
--- On Sun, 4/12/09, Ross Mellgren <[email protected]> wrote:
From: Ross Mellgren <[email protected]>
Subject: Re: [Haskell-cafe] Functions that return functions
To: "michael rice" <[email protected]>
Cc: "Daniel Fischer" <[email protected]>, [email protected]
Date: Sunday, April 12, 2009, 9:23 PM
Under the covers of syntax they only have one parameter, but you can
write curried lambdas or functions easily:
\ a b -> a + b
which is equivalent to
\ a -> \ b -> a + b
and also equivalent to the "normal" function syntax
f a b = a + b
or
f a = \ b -> a + b
-Ross
On Apr 12, 2009, at 9:09 PM, michael rice wrote:
My question was meant in the context of the makeVerifier function,
which is passed a lambda expression. It's my understanding that
Haskell lambda expressions can have only a single parameter, which
is why I changed the function parameter to a pair, (i,d).
How would it be done otherwise?
Michael
--- On Sun, 4/12/09, Daniel Fischer <[email protected]> wrote:
From: Daniel Fischer <[email protected]>
Subject: Re: [Haskell-cafe] Functions that return functions
To: "michael rice" <[email protected]>
Cc: [email protected]
Date: Sunday, April 12, 2009, 7:20 PM
Am Montag 13 April 2009 01:09:22 schrieb michael rice:
> Example please.
>
> Michael
>
Curried:
f :: a -> b -> c
amenable to partial application.
Uncurried:
g :: (a,b) -> c
not easy to apply partially.
The Prelude contains
curry :: ((a,b) -> c) -> (a -> b -> c)
uncurry :: (a -> b -> c) -> ((a,b) -> c)
to convert if needed.
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