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Today's Topics:
1. Matrix and types (mike h)
2. Re: Matrix and types (Francesco Ariis)
----------------------------------------------------------------------
Message: 1
Date: Thu, 14 Mar 2019 11:10:06 +0000
From: mike h <mike_k_hough...@yahoo.co.uk>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: [Haskell-beginners] Matrix and types
Message-ID: <f25f3321-f7ac-4b57-97f3-e4b340e10...@yahoo.co.uk>
Content-Type: text/plain; charset="utf-8"
Hi,
As an exercise I want to write a Matrix library.
Multiplication of two matrices is only defined when the the number of columns
in the first matrix
equals the number of rows in the second matrix. i.e. c1 == r2
So when writing the multiplication function I can check that c1 == r2 and do
something.
However what I really want to do, if possible, is to have the compiler catch
the error.
I’d appreciate any advice on how to approach this. I don’t want a full
description of exactly what to do as that way I won’t have struggled or argued
with the compiler - which for me is the best way to learn Haskell :)
Thanks
Mike
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Message: 2
Date: Thu, 14 Mar 2019 12:37:20 +0100
From: Francesco Ariis <fa...@ariis.it>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Matrix and types
Message-ID: <20190314113720.xim35mdypfxxq...@x60s.casa>
Content-Type: text/plain; charset=us-ascii
Hello Mike,
On Thu, Mar 14, 2019 at 11:10:06AM +0000, mike h wrote:
> Multiplication of two matrices is only defined when the the number of columns
> in the first matrix
> equals the number of rows in the second matrix. i.e. c1 == r2
>
> So when writing the multiplication function I can check that c1 == r2 and do
> something.
> However what I really want to do, if possible, is to have the compiler catch
> the error.
Type-level literals [1] or any kind of similar trickery should help you
with having matrices checked at compile-time.
[1]
https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/type-level-literals.html
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