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Today's Topics:
1. Trying to understand the foldl type? (Angus Comber)
2. Re: Trying to understand the foldl type? (Bob Ippolito)
3. Re: Trying to understand the foldl type? (Kim-Ee Yeoh)
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Message: 1
Date: Tue, 24 Dec 2013 13:19:42 +0000
From: Angus Comber <[email protected]>
To: Haskell Beginners <[email protected]>
Subject: [Haskell-beginners] Trying to understand the foldl type?
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The type is:
foldl :: (a -> b -> a) -> a -> [b] -> a
Eg I might do something like this:
foldl (+) 0 [1..10]
so taking (a -> b -> a)
leftmost a is (+)
b is 0
right a is what? The first value in the list?
Then -> ?
[b] ? Is this like the temporary recursion calculation?
final -> a is the result?
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Message: 2
Date: Tue, 24 Dec 2013 05:47:23 -0800
From: Bob Ippolito <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Trying to understand the foldl type?
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Given foldl (+) 0 [1..10]
(+) is (a -> b -> a)
0 is a
[1..10] is [b]
and the final a is the result of the expression.
On Tuesday, December 24, 2013, Angus Comber wrote:
> The type is:
>
> foldl :: (a -> b -> a) -> a -> [b] -> a
>
> Eg I might do something like this:
>
> foldl (+) 0 [1..10]
>
> so taking (a -> b -> a)
>
> leftmost a is (+)
> b is 0
> right a is what? The first value in the list?
>
> Then -> ?
>
> [b] ? Is this like the temporary recursion calculation?
>
> final -> a is the result?
>
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Message: 3
Date: Tue, 24 Dec 2013 22:21:52 +0700
From: Kim-Ee Yeoh <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Trying to understand the foldl type?
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<CAPY+ZdSddOwVmxdqLsPaF62V47aXtB=refbyxk0hat+ux4s...@mail.gmail.com>
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On Tue, Dec 24, 2013 at 8:19 PM, Angus Comber <[email protected]> wrote:
> foldl :: (a -> b -> a) -> a -> [b] -> a
>
> Eg I might do something like this:
>
> foldl (+) 0 [1..10]
>
Try the following in ghci to see if you get an idea of what's going on:
:t foldl
:t foldl (+)
:t foldl (+) 0
:t foldl (+) 0 [1..10]
-- Kim-Ee
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