Editing The I/O problem (section)

== Other questions ==

* Is the C language "purely functional"?

::No:
::* C isn't "pure" - it allows unrestricted access to observable effects, including those of I/O.
::* C isn't "functional" - it was never intended to be [[Referential transparency|referentially transparent]], which severely restricts the ability to use [[Equational reasoning examples|equational reasoning]].

* Is the Haskell language "purely functional"?

::[https://chadaustin.me/2015/09/haskell-is-not-a-purely-functional-language Haskell is not a purely functional language], but is often described as being referentially transparent.

* Why do our programs need to read input and write output?

::Because programs are usually written for practical purposes, such as implementing domain-specific [https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.7.2089&rep=rep1&type=pdf little languages] like [https://dhall-lang.org Dhall].

* All of this and still no formal mathematical or logical argument?
::{|
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According to Church's Thesis:

<blockquote>
[...] any <i>intuitively</i>
calculable function is also calculable within any of
[Post's, Kleene's, Church's, Turing's, or Markov's] mathematical
frameworks of calculability or computability.

:<small>[https://www.eecs.yorku.ca/~tgeorge/papers/churchs-thesis.pdf A user-friendly Introduction to (un)Computability and Unprovability via “Church’s Thesis”], George Tourlakis (first page).</small> <!-- 2011 -->
</blockquote>

So what exactly is an "<i>intuitively</i> calculable function"?
|}