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Exotic Programming Ideas, Part 3: Effect Systems

stephendiehl.com

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Re: Exotic Programming Ideas, Part 3: Effect Systems

#3

Post by siraben »

I highly recommend Oleg Kiselyov's talk titled "Having an Effect"[0] in which he talks about

- purely functional model of computation and its pitfalls

- Actor model, effectful programming with requests and responses and an implementation in Haskell.

- denotational semantics and combining effects. Once you have a model of your language, what if you want to extend it by adding another effect? It forces you to rewrite the semantics (and thus any interpreter of your language) completely. Taking using the effects-as-requests viewpoint, only the request and handler for an effect needs to be added or changed, and the rest untouched. This is known as "stable denotations".

- really evaluating what it means for an expression to be pure or effectful. Even variable reference should be considered an effect.

- different scoping rules in lambda calculus can be expressed in terms of effects! Creating a dynamic closure is not effectful, though applying it usually is, OTOH, creating a lexical closure is effectful but using it is not.

I think Haskell provides a good example of how a purely functional language can still express effectful computation. through a monadic interface. Though monad transformers have their share of problems when heavily nested (n^2 instances, performance), various effect system libraries are gaining traction.[2] On the bleeding edge of research there's languages like Frank[1] where the effect system is pervasive throughout the language.

[0] https://www.youtube.com/watch?v=GhERMBT7u4w

[1] https://github.com/frank-lang/frank

[2] Implementing free monads from scratch, https://siraben.github.io/2020/02/20/free-monads.html

Re: Exotic Programming Ideas, Part 3: Effect Systems

#4

Post by cultus »

siraben wrote: post #3

I highly recommend Oleg Kiselyov's talk titled "Having an Effect"[0] in which he talks about - purely functional model of computation and its pitfalls - Actor model, effectful programming with requests and responses and an implementation in Haskell. - denotational semantics and combining effects. Once you have a model of your language, what if you want to extend it by adding another effect? It forces you to rewrite t…

Also see Oleg's "Effects without Monads: Non-determinism -- Back to the Meta-Language"

https://arxiv.org/abs/1905.06544

Re: Exotic Programming Ideas, Part 3: Effect Systems

#5

Post by merelydev »

siraben wrote: post #3

I highly recommend Oleg Kiselyov's talk titled "Having an Effect"[0] in which he talks about - purely functional model of computation and its pitfalls - Actor model, effectful programming with requests and responses and an implementation in Haskell. - denotational semantics and combining effects. Once you have a model of your language, what if you want to extend it by adding another effect? It forces you to rewrite t…

Source: https://www.reddit.com/r/programming/comments/7wbtg/who_is_o...

   - Oleg eats lambdas for breakfast

   - The Y combinator fears Oleg

   - Oleg knows all the programs that halt on a Turing machine

   - Oleg is the guy that Chuck Norris goes to when he has an algorithm complexity question

   - Oleg reprograms his own DNA with Scheme macros

   - All of Oleg's Haskell programs are well-typed by definition

   - Oleg can read C++ compiler error messages.

   - Oleg built his house out of Prolog relations

   - Oleg speaks machine lanugage

   - Oleg once turned a zero into a one.

   - Emacs? Vi? Oleg wills files into existance

   - Oleg has the Haskell98 Report memorized. In Binary. In UTF-EBCDIC

   - Oleg can write unhygienic syntax-rules macros.

   - Sometimes Recursion gets confused when Oleg uses it.

Re: Exotic Programming Ideas, Part 3: Effect Systems

#6

Post by skybrian »

I expect that, as with any other type system extension, the more granular your effects are, the more likely you are to run into a “what color is my function” problem. If you have a public API that declares certain effects, you’re stuck with those unless you break backward compatibility.

In a practical system, when writing a library and especially an abstract interface, you’d want to be careful what you promise and declare effects that you might need (but currently don’t use), just in case you will need them later.

It’s not that easy even to distinguish functions that can fail from those that can’t, if you’re trying to anticipate how a system will evolve. Something that’s in-memory now might change to being done over the network later.

Re: Exotic Programming Ideas, Part 3: Effect Systems

#7

Post by patrec »

merelydev wrote: post #5
siraben wrote: post #3

I highly recommend Oleg Kiselyov's talk titled "Having an Effect"[0] in which he talks about - purely functional model of computation and its pitfalls - Actor model, effectful programming with requests and responses and an implementation in Haskell. - denotational semantics and combining effects. Once you have a model of your language, what if you want to extend it by adding another effect? It forces you to rewrite t…

Source: https://www.reddit.com/r/programming/comments/7wbtg/who_is_o... - Oleg eats lambdas for breakfast - The Y combinator fears Oleg - Oleg knows all the programs that halt on a Turing machine - Oleg is the guy that Chuck Norris goes to when he has an algorithm complexity question - Oleg reprograms his own DNA with Scheme macros - All of Oleg's Haskell programs are well-typed by definition - Oleg can read C++ comp…

> Oleg can write unhygienic syntax-rules macros.

Not only can he do it, he even wrote a paper about it: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.36...

Re: Exotic Programming Ideas, Part 3: Effect Systems

#9

Post by tomp »

PaulHoule wrote: post #2

"Non-termination is an Effect"

I never understood this one. I mean obviously a kind compiler should warn you against using

    while true { }
and

    while i
but in general, I don’t find distinction between “this infinite loop terminates” (e.g. an event loop) and “this code obviously terminates but not in the lifetime of this universe” (e.g. computing Ackermann(5)) to be that useful.

Re: Exotic Programming Ideas, Part 3: Effect Systems

#10

Post by siraben »

patrec wrote: post #7
merelydev wrote: post #5

Earlier quoted context omitted.

Source: https://www.reddit.com/r/programming/comments/7wbtg/who_is_o... - Oleg eats lambdas for breakfast - The Y combinator fears Oleg - Oleg knows all the programs that halt on a Turing machine - Oleg is the guy that Chuck Norris goes to when he has an algorithm complexity question - Oleg reprograms his own DNA with Scheme macros - All of Oleg's Haskell programs are well-typed by definition - Oleg can read C++ comp…

> Oleg can write unhygienic syntax-rules macros. Not only can he do it, he even wrote a paper about it: https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.36...

IMO implementing hygienic macros properly is one of the hardest tasks in programming languages, especially since variable capture can cause subtle bugs.
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