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== Denotative languages and the I/O problem ==
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Let's assume:
* a denotative language exists - here, it's called <i>DL</i>.
* the implementation of <i>DL</i> is written in an imperative language - let's call that <i>IL</i>.
Let's also assume:
* <i>DL</i> is initially successfull.
* solid-state Turing machines remain in use, so <i>IL</i> is still needed.
As time goes on, technology advances which means an ever-expanding list of hardware to cater for. Unfortunately, the computing architecture remains mired in state and effects - supporting the new hardware usually means a visit to <i>IL</i> to add the extra subroutines/procedures (or modify existing ones) in the implementation.
<i>DL</i> will still attract some interest:
* Parts of the logic required to support hardware can be more usefully written as <i>DL</i> definitions, to be called by the implementation where needed - there's no problem with imperative code calling denotative code.
* periodic refactoring of the implementation reveals suitable candidates for replacement with calls to <i>DL</i> expressions.
* <i>DL</i> is occasionally extended to cater for new patterns of use - mostly in the form of new abstractions and their supporting libraries, or (more rarely) the language itself and therefore its implementation in <i>IL</i>.
...in any case, <i>DL</i> remains denotative - if you want a computer to do something new to its surroundings, that usually means using <i>IL</i> to modify the implementation of <i>DL</i>.
So the question is this: which language will programmers use more often, out of habit - <i>DL</i> or <i>IL</i>?
Here's a clue:
<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
They [monadic types] are especially useful for structuring large systems. In fact, there's a danger of programming in this style too much (I know I do), and almost forgetting about the 'pure' style of Haskell.
<tt>Noel Winstanley, 1999.</tt>
Instead of [http://conal.net/blog/posts/can-functional-programming-be-liberated-from-the-von-neumann-paradigm looking at the whole system in a consistently denotational style (with simple & precise semantics)] by using <i>DL</i> alone, most users would be working on the implementation using <i>IL</i> - being denotative makes for nice libraries, but getting the job done means being imperative. Is this an improvement over the current situation in Haskell? No - instead of having the denotative/imperative division in Haskell by way of types, users would be contending with that division <i>at the language level</i> in the forms of differing syntax and semantics, annoying foreign calls, and so forth.
The advent of Haskell's FFI is an additional aggravation - it allows countless more effect-centric operations to be accessed. Moving <b>all</b> of them into a <i>finite</i> implementation isn't just impractical - it's impossible.
But if you still think being denotative is worth all that bother (or you just want to prove me wrong :-) [https://www.ioccc.org/2019/lynn/hint.html this] could be a useful place to start:
<div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
* <tt>OneHundredPercentPure</tt>: Gone is the catch-all lawless <code>IO</code> monad. And no trace of those scary <code>unsafeThisAndThat</code> functions. All functions must be pure.
&mdash; [[User:Atravers|Atravers]] Fri Oct 22 06:36:41 UTC 2021

Latest revision as of 07:30, 3 March 2022

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