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| == Denotative languages and the I/O problem ==
| | There is currently no text in this page. |
| | | You can <span style="color:brown;">search for this page title</span> in other pages, |
| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
| | <span style="color:brown;">search the related logs</span>, |
| My view is that the next logical step for programming is to split into two non-overlapping programming domains:
| | or <span style="color:brown;">create this page</span>. |
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| * runtime building for …
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| * … mathematical programming languages
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| <tt>[https://www.haskellforall.com/2021/04/the-end-of-history-for-programming.html Gabriella Gonzalez].</tt>
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| </div>
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| Let's assume:
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| * a denotative language exists - here, it's called <i>DL</i>.
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| * the implementation of <i>DL</i> is written in an imperative language - let's call that <i>IL</i>.
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| Let's also assume:
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| * <i>DL</i> is initially successfull.
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| * solid-state Turing machines remain in use, so <i>IL</i> is still needed.
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| 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.
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| <i>DL</i> will still attract some interest:
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| * 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.
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| * periodic refactoring of the implementation reveals suitable candidates for replacement with calls to <i>DL</i> expressions.
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| * <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>.
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| ...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>.
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| So the question is this: which language will programmers use more often, out of habit - <i>DL</i> or <i>IL</i>?
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| Here's a clue:
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| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
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| 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.
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| <tt>[[Monad tutorials timeline|Noel Winstanley]].</tt>
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| </div>
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| 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.
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| 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.
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| 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:
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| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
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| * <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.
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| </div>
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| — [[User:Atravers|Atravers]] Fri Oct 22 06:36:41 UTC 2021
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| == Outsourcing the I/O problem ==
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| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote">
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| '''4 Compiling Agda programs'''
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| This section deals with the topic of getting Agda programs to interact
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| with the real world. Type checking Agda programs requires evaluating
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| arbitrary terms, ans as long as all terms are pure and normalizing this is
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| not a problem, but what happens when we introduce side effects? Clearly,
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| we don't want side effects to happen at compile time. Another question is
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| what primitives the language should provide for constructing side effecing
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| programs. In Agda, these problems are solved by <i>allowing arbitrary
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| Haskell functions to be imported as axioms.</i> At compile time, these imported
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| functions have no reduction behaviour, <i>only at run time is the
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| Haskell function executed</i>.
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| <tt>[http://www.cse.chalmers.se/~ulfn/papers/afp08/tutorial.pdf Dependently Typed Programming in Agda], Ulf Norell and James Chapman [<i>emphasis added</i>].</tt>
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| </div>
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| In Haskell:
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| * just extend the FFI enough to replace the ''usually''-abstract I/O definitions with calls to foreign definitions:
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| :{|
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| |<haskell>
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| instance Monad IO where
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| return = primUnitIO
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| (>>=) = primBindIO
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|
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| foreign import ccall unsafe primUnitIO :: a -> IO a
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| foreign import ccall unsafe primBindIO :: IO a -> (a -> IO b) -> IO b
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| ⋮
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| </haskell>
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| |}
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| * the <code>IO</code> type is then just a type-level tag, as specified in the Haskell 2010 report:
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| :{|
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| |<haskell>
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| data IO a -- that's all folks!
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| </haskell>
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| |}
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| ''Voilà!'' In this example, the I/O problem has been outsourced to C - if you're not happy with C's solution to the I/O problem, just use another programming language for the Haskell implementation: there's plenty of them to choose from (...but don't use Haskell, to avoid going <code>⊥</code>-up ;-).
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| By defining them in this way, <code>IO</code> and its actions in Haskell can also be thought of as being "axiomatic": they have no effect when a Haskell program is compiled, only at run time is the foreign definition executed and its effects occur.
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| — [[User:Atravers|Atravers]] Thu Dec 9 01:55:47 UTC 2021
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| == Mathematics and the I/O problem ==
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| Mathematics is abstract:
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| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote"> | |
| In a preliminary sense, mathematics is abstract because it is studied using highly general and formal resources.
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| <tt>[https://iep.utm.edu/math-app The Applicability of Mathematics], from the [https://iep.utm.edu/Internet Encyclopedia of Philosophy].</tt>
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| </div>
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| In particular, it abstracts from the existence of an external environment. This poses a challenge for languages like Haskell which pursue the mathematical notion of a function (rather than use subroutines or procedures):
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| <div style="border-left:1px solid lightgray; padding: 1em" alt="blockquote"> | |
| How must interactions between a program and an external environment (consisting of, e.g., input/output-devices, file systems, ...) be described in a programming language that abstracts from the existence of an outside world?
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| <tt>[https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.95.9846&rep=rep1&type=pdf Funtions, Frames and Interactions], Claus Reinke (page 10 of 210).</tt>
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| </div>
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| So the seeking of a "pure"/"mathematical"/"functional"/"formal"/... '''general-purpose''' solution to I/O which <u>isn't</u> [https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.13.9123&rep=rep1&type=pdf awkward] should focus on finding an extension of mathematics which can [https://www.cs.kent.ac.uk/people/staff/dat/krc/paraffins-turner.pdf elegantly] describe interactions with external environments:
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| * If one exists, denotational semantics can then be used to map it into Haskell.
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| * If one cannot exist (like the solution to the halting problem), then implementors everywhere can just select the most-suitable (or least-ugly) model of I/O as they see fit.
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| — [[User:Atravers|Atravers]] Fri Jan 28 22:33:43 UTC 2022
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