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Today's Topics:
1. Evaluation oddity (Torsten Otto)
2. Re: Evaluation oddity (Francesco Ariis)
----------------------------------------------------------------------
Message: 1
Date: Sun, 6 Feb 2022 19:00:41 +0100
From: Torsten Otto <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Evaluation oddity
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hi all,
maybe one of you sees a difference, I sure don’t… The full code for this is
below.
When I call
*Main> diffieH 23 16 20
13
and use the result in
*Main> encipher "abc" 13
„nop"
I get the letters to be expected. However, when I combine these into
> start text p a b = encipher text (diffieH p a b)
*Main> start "abc" 23 16 20
„efg"
the result changes.
Any hints are most welcome.
Thank you and regards
Torsten
> import Data.Char
> diffieH p a b = (b ^ a) `mod` p
> number2letter number = chr (number + 96)
> letter2number letter = (ord letter) - 96
> start text p a b = encipher text (diffieH p a b)
> encipher [] _ = []
> encipher (b:rest) key = (number2letter (((letter2number b)+key) `mod` 26))
> : (encipher rest key)
------------------------------
Message: 2
Date: Sun, 6 Feb 2022 20:02:47 +0100
From: Francesco Ariis <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Evaluation oddity
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hello Otto,
Il 06 febbraio 2022 alle 19:00 Torsten Otto ha scritto:
> When I call
>
> *Main> diffieH 23 16 20
> 13
>
> and use the result in
>
> *Main> encipher "abc" 13
> „nop"
>
> I get the letters to be expected. However, when I combine these into
>
> > start text p a b = encipher text (diffieH p a b)
>
> *Main> start "abc" 23 16 20
> „efg"
>
> the result changes.
You should always write top level signatures by hand in your
code. What is the signature that you want for `diffieH`?
This is the inferred one
λ> :t diffieH
diffieH :: (Integral a, Integral b) => a -> b -> a -> a
------------------------------
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