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Lambda Jam 2014 - Eric Meijer - The Lost Art of Denotational Semantics #YOWLambdaJam

YOW! Conferences · Youtube · 7 HN points · 2 HN comments
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Youtube Summary
Denotational Semantics, in this context the art of crafting interpreters for a given programming language using a purely functional meta-language http://people.cis.ksu.edu/~schmidt/text/densem.html, was one of the very first applications of functional programming, with Christopher Strachey as one of the world’s earliest FP hackers.

By studying Denotational Semantics we gain deep insights into programming languages while at the same time learning numerous cool and practical programming tricks. For example monads found their way from pure Category Theory via Denotational Semantics into contemporary programming languages. And those that are actually enjoying writing callbacks with lambda expressions in Node.js, are believe it or not, using a technique that was invented more than half a century ago by theoreticians to model GOTOs in programming languages. Algebraic datatypes and folds? Those must be recent innovations! Nope, Strachey, Scott, and Stoy were using those long before most of us were even born. In short, a thorough understanding of Denotational Semantics is a necessary condition to reach FP mastery.

In this talk we start with a StackOverflow question about the semantics of try-catch-finally in Scala, and spell out in detail how this widely used, but often poorly understood language feature works by providing a concise continuation semantics. Next we show how try-catch-finally is nothing more than a web of gotos and global variables by defunctionalizing our semantics to generate assembly code.

Operational Semantics, the craft of defining abstract machines for a given programming language using a purely functional meta-language, is the dual of Denotational Semantics. Unfortunately, that is a topic we will have to leave for a future talk.
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Hacker News Stories and Comments

All the comments and stories posted to Hacker News that reference this video.
May 21, 2017 · 2 points, 0 comments · submitted by tosh
Dec 13, 2016 · 4 points, 0 comments · submitted by tosh
May 17, 2015 · 1 points, 0 comments · submitted by bbcbasic
It is absolutely marketing talk, there's other established terms for what that means but they elected to make up other terms. Perhaps they should take the lesson from this talk where they explicitly break down this exact term and explain what they REALLY mean in common terms.

https://www.youtube.com/watch?v=pOl4E8x3fmw

rtb
> there's other established terms for what that means

Please could you expand on this?

Regarding duality - obligatory meijer reference - this time on async and observables. main point: any one design could very well be isomorphic to a whole range of options in the design space - https://www.youtube.com/watch?v=pOl4E8x3fmw&feature=youtu.be...
enord
Also regarding duality - just because there is a proof of duality between designs it does not follow that they design the same thing at all.

Classic example from CT: In sets (well, the category of sets and maps but still...), the cartesian product is dual to the disjoint union (sum type, variant record etc.) From this, anything proven about cartesian products (which is a lot, as it is fundamental to most of set-theory) proves something about the disjoint union through the duality. What it actually proves about disjouint unions is open to interpretation on a proof by proof basis.

Which is to say: The consequences of duality are rich and powerful, but they are often non-obvious and for systems with many moving parts almost certainly non-trivial.

platz
Good point
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