From t-otto-news at gmx.de  Sun Feb  6 18:00:41 2022
From: t-otto-news at gmx.de (Torsten Otto)
Date: Sun, 6 Feb 2022 19:00:41 +0100
Subject: [Haskell-beginners] Evaluation oddity
Message-ID: <7345CFA8-899B-4331-88A6-6D5E8F04F7A5@gmx.de>

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)


From fa-ml at ariis.it  Sun Feb  6 19:02:47 2022
From: fa-ml at ariis.it (Francesco Ariis)
Date: Sun, 6 Feb 2022 20:02:47 +0100
Subject: [Haskell-beginners] Evaluation oddity
In-Reply-To: <7345CFA8-899B-4331-88A6-6D5E8F04F7A5@gmx.de>
References: <7345CFA8-899B-4331-88A6-6D5E8F04F7A5@gmx.de>
Message-ID: <YgAbVz7hbU1lXLd3@mkiii.casa>

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