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Today's Topics:
1. Re: Function to compute the mean (David James)
----------------------------------------------------------------------
Message: 1
Date: Mon, 10 May 2021 11:43:03 +0000
From: David James <dj112...@outlook.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Function to compute the mean
Message-ID:
<am6pr04mb42141e9503a0db6e717c02aeb6...@am6pr04mb4214.eurprd04.prod.outlook.com>
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Hello – I wanted to add some comments. mean is as you describe.
mean1 as defined can take a list of any Real type, and return any Fractional
type. These types need not be the same, and it’s up to the *caller* of mean1 to
say what types they want to give and get returned, e.g. the following is
possible:
> :m +Data.Ratio
> :m +Data.Complex
> mean1 [6%5, 2%3] :: Complex Double
0.9333333333333333 :+ 0.0
This may not be what you were expecting, and maybe you want something like this:
mean2 :: (Fractional a) => [a] -> a
mean2 xs = sum xs / genericLength xs
(and note the realToFrac is then unces
From: Beginners <beginners-boun...@haskell.org> on behalf of Joe King
<joeking1...@yahoo.com>
Sent: Saturday, May 8, 2021 10:39:50 AM
To: beginners@haskell.org <beginners@haskell.org>
Subject: [Haskell-beginners] Function to compute the mean
Greeetings I am new here and pretty new to Haskell.
I was wondering what are the relative advanatges/disadvatnages of specifying a
mean function in these two ways:
mean :: [Double] -> Double
mean xs = sum xs / fromIntegral (length xs)
and
mean1 :: (Real a, Fractional b) => [a] -> b
mean1 xs = realToFrac (sum xs) / genericLength xs
I understand that mean1 has the advantage that it can be called with lists of
any Real type, so would work with things like
foo :: [Int]
foo = [1,2,3]
mean foo
-- type mismatch error
mean1 foo
-- no error
But suppose that I know I will only ever use lists of Double, is there still
any advantage (or disadvantage of using mean1). For example is there any
performance benefit by using mean in that case since mean1 has additional
function evaluation.
Are there any other considerations ?
Thanks in advance
JK
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