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Today's Topics:
1. Int and Integer (Peter Normington)
2. Re: Int and Integer (Theodore Lief Gannon)
3. Re: Int and Integer (Peter Normington)
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Message: 1
Date: Sun, 17 Dec 2017 13:48:44 +0000
From: Peter Normington <pe...@ireby.org.uk>
To: beginners@haskell.org
Subject: [Haskell-beginners] Int and Integer
Message-ID:
<capksagqzkkfenfk_z5yvvdfsy_jykauvkjdexlae7fbo+_s...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Why do I get an error in the following example:
memoized_fib :: Integer -> Integer
memoized_fib = (map fib [0 ..] !!)
where fib 1 = 1
fib 2 = 1
fib n = memoized_fib (n-2) + memoized_fib (n-1)
but not in:
memoized_fib :: Int -> Integer
memoized_fib = (map fib [0 ..] !!)
where fib 1 = 1
fib 2 = 1
fib n = memoized_fib (n-2) + memoized_fib (n-1)
?
The error is reported by GHCi as:
error:
• Couldn't match type ‘Integer’ with ‘Int’
Expected type: Integer -> Integer
Actual type: Int -> Integer
• In the expression: (map fib [0 .. ] !!)
In an equation for ‘memoized_fib’:
memoized_fib
= (map fib [0 .. ] !!)
where
fib 1 = 1
fib 2 = 1
fib n = memoized_fib (n - 2) + memoized_fib (n - 1)
|
2 | memoized_fib = (map fib [0 ..] !!)
| ^^^^^^^^^^^^^^^^^
Failed, 0 modules loaded.
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Message: 2
Date: Sun, 17 Dec 2017 07:40:54 -0800
From: Theodore Lief Gannon <tan...@gmail.com>
To: pe...@ireby.org.uk, The Haskell-Beginners Mailing List -
Discussion of primarily beginner-level topics related to Haskell
<beginners@haskell.org>
Subject: Re: [Haskell-beginners] Int and Integer
Message-ID:
<cajopsuddgkhnmgwpqbvzmfkv4pblj9oxm+j_fzqtq77zmet...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Because:
(!!) :: [a] -> Int -> a
On Dec 17, 2017 5:50 AM, "Peter Normington" <pe...@ireby.org.uk> wrote:
> Why do I get an error in the following example:
>
> memoized_fib :: Integer -> Integer
> memoized_fib = (map fib [0 ..] !!)
> where fib 1 = 1
> fib 2 = 1
> fib n = memoized_fib (n-2) + memoized_fib (n-1)
>
> but not in:
>
> memoized_fib :: Int -> Integer
> memoized_fib = (map fib [0 ..] !!)
> where fib 1 = 1
> fib 2 = 1
> fib n = memoized_fib (n-2) + memoized_fib (n-1)
> ?
>
> The error is reported by GHCi as:
>
> error:
> • Couldn't match type ‘Integer’ with ‘Int’
> Expected type: Integer -> Integer
> Actual type: Int -> Integer
> • In the expression: (map fib [0 .. ] !!)
> In an equation for ‘memoized_fib’:
> memoized_fib
> = (map fib [0 .. ] !!)
> where
> fib 1 = 1
> fib 2 = 1
> fib n = memoized_fib (n - 2) + memoized_fib (n - 1)
> |
> 2 | memoized_fib = (map fib [0 ..] !!)
> | ^^^^^^^^^^^^^^^^^
> Failed, 0 modules loaded.
>
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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Message: 3
Date: Sun, 17 Dec 2017 16:15:37 +0000
From: Peter Normington <pe...@ireby.org.uk>
To: Theodore Lief Gannon <tan...@gmail.com>
Cc: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Int and Integer
Message-ID:
<capksagqz8mealzw-xoy7lbd-sbz3uy_c3vjgfs16b8v2cxl...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thanks, Theodore. As simple as that!
Best regards,
Peter
On 17 December 2017 at 15:40, Theodore Lief Gannon <tan...@gmail.com> wrote:
> Because:
> (!!) :: [a] -> Int -> a
>
> On Dec 17, 2017 5:50 AM, "Peter Normington" <pe...@ireby.org.uk> wrote:
>
>> Why do I get an error in the following example:
>>
>> memoized_fib :: Integer -> Integer
>> memoized_fib = (map fib [0 ..] !!)
>> where fib 1 = 1
>> fib 2 = 1
>> fib n = memoized_fib (n-2) + memoized_fib (n-1)
>>
>> but not in:
>>
>> memoized_fib :: Int -> Integer
>> memoized_fib = (map fib [0 ..] !!)
>> where fib 1 = 1
>> fib 2 = 1
>> fib n = memoized_fib (n-2) + memoized_fib (n-1)
>> ?
>>
>> The error is reported by GHCi as:
>>
>> error:
>> • Couldn't match type ‘Integer’ with ‘Int’
>> Expected type: Integer -> Integer
>> Actual type: Int -> Integer
>> • In the expression: (map fib [0 .. ] !!)
>> In an equation for ‘memoized_fib’:
>> memoized_fib
>> = (map fib [0 .. ] !!)
>> where
>> fib 1 = 1
>> fib 2 = 1
>> fib n = memoized_fib (n - 2) + memoized_fib (n - 1)
>> |
>> 2 | memoized_fib = (map fib [0 ..] !!)
>> | ^^^^^^^^^^^^^^^^^
>> Failed, 0 modules loaded.
>>
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
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