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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: How to get Ada to ?cross the chasm??
Date: Thu, 10 May 2018 14:16:09 +0300
Organization: Tidorum Ltd
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Xref: reader02.eternal-september.org comp.lang.ada:52199
Date: 2018-05-10T14:16:09+03:00
List-Id: <comp.lang.ada>

On 18-05-09 00:31 , Paul Rubin wrote:
> Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>>>     x = 1 : 2 : 3 : x
>> Can you construct such a list in Haskell without using and setting
>> explicit references?
>
> If you mean writing the list without using x on both sides of the equal
> sign, you could use a fixpoint combinator:
>
>     Prelude Control.Monad.Fix> let f = fix ([1,2,3]++)
>     Prelude Control.Monad.Fix> take 20 f
>     [1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2,3,1,2]
>
> But fix is written something like this:
>
>    fix f = x where x = f x
>
> and there's an explicit reference there.

Thanks, this explains it.

> There's an argument for eliminating unrestricted recursion from
> programming so that all functions must eventually return, ...
>
> http://www.jucs.org/jucs_10_7/total_functional_programming

Interesting, especially the places where some appeal is made to 
quantitative termination (complexity) properties. The fact about the 
limitations of languages where all programs necessarily terminate, and 
the consequent need for a hierarchy of languages, were new to me.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .