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An insight that might help tie functional programming (FP) and imperative programming (IP) together is that FP is spreadsheets and IP is macros (edit: recording

An insight that might help tie functional programming (FP) and imperative programming (IP) together is that FP is spreadsheets and IP is macros (edit: recordings of human interaction and shell scripts). Ideally all business logic should be FP and event-driven interfaces are usually IP. I think of these as clusters of similar concepts: FP synchronous blocking immutable process isolation auto optimization auto parallelization higher-order methods scatter-gather, fork-join deterministic/repeatable (sometimes) reversable execution models and views in MVC ugly prefix/postfix syntax that doesn't look like algebra (not always) IP asynchronous nonblocking mutable shared state manual optimization manual parallelization generators/iterators threads, locks/mutexes nondeterministic promises/futures requiring snapshots to reverse execution controllers in MVC pretty infix syntax that looks like algebra (not always) I believe that ideally we'd write everything in FP with no IP whatsoever. So no mutable variables, no pass by reference, no iteration. Just higher-order methods and copy-on-write, with static analysis simplifying intermediate code into its fastest and/or most concise representation to run in parallel as fast as possible on multicore CPUs. Each component runs single-shot using analogs of STDIN/STDOUT/STDERR. These can fully represent models and views functionally and even declaratively. Then IP would be used to wire up components, similarly to controllers in MVP. For example when a UNIX executable blocks waiting for more data on an input stream, or more room in an output stream. The runtime/filesystem/network/OS between isolated executables is imperative. FP and IP can be unified by enforcing immutability everywhere in an IP language, then transpiling the code to reshape it between prefix/infix/postfix notation. Unfortunately I/O still can't be implemented without monads, making this psuedo-FP language impure. So there may be no way to build an entirely pure FP runtime that can respond to dynamic input/output and exceptional behavior. It would be like having a spreadsheet with no connection to the outside world, where the values of cells can't be edited, so formulas could run but they never have reason to do so. Attempts can also be made to eliminate IP altogether by providing impure functionality in FP languages by introducing monads for I/O and exceptional behavior, allowing mutation by isolating it in blocks, etc. I believe that makes impure FP languages equivalent to IP, corrupting them and defeating the point of using FP. Sometimes that makes sense though if/when we can live with the tradeoffs, or if we're porting code from IP languages that's too difficult to refactor to pure FP. Unfortunately most impure FP languages are also difficult to read by humans, limiting their adoption. Without the basic understanding listed here, the world seems to naturally head towards IP, since it most closely mimicks how humans navigate the world. IP languages tend to borrow FP concepts like monads to implement async behavior like generators, futures and promises. This sacrifices determinism and expands shared state to such a degree that IP programs can only grow to a certain size before they are intractable. This can sort of be avoided with reducers like Redux or writelog databases, usually at a cost in having to maintain boilerplate. The world also tends to double down on static types, categories, templates/generics, formal contracts/interfaces, etc, borrowed from FP without a clear understanding of when or why they're necessary. When often programs can be written much more concisely and clearly by avoiding custom types altogether and focusing on data-driven standard types like numbers, strings and JSON run through transformation functions. An obvious example being how Java programs are often bloated and overengineered because they are object-oriented instead of functional. It's amazing to see how so much boilerplate often contains so little actual business logic. And how languages inspired by Java, like C#, often seem to repeat its shortcomings. I think of all of this as analogous to how beginners tend to implement a game's main loop with state machines for each sprite. Whereas in Unity they can use coroutines. Once we see how straightforward it is to write business logic in a one-shot fashion, it's hard to imagine going back to juggling the complexities of state machines. Especially since state machines and coroutines can be made equivalent via generators. Another example is that digital electronic circuits are equivalent to a spreadsheet and can be represented and analyzed by FP, but it's hard to convert an IP program description into a circuit or analyze its behavior formally using techniques from logic. Once we have these kinds of insights, it's difficult to unsee them. And to look at best practices without asking ourselves why we're doing things the hard way. As far as I know, the only language that approximates pure FP with IP glue handled by the runtime to avoid monads is ClojureScript. Admittedly, I'm probably misunderstanding how it works.

ryandv 2y ago
> I believe that ideally we'd write everything in FP with no IP whatsoever. So no mutable variables, no pass by reference, no iteration. > Then IP would be used to wire up components, similarly to controllers in MVP. This viewpoint was popularized by Gary Bernhardt a while ago as "functional core, imperative shell." [0] Functional paradigms should be used for expressing core logic and transformation of data; code written in this style is side-effect free, "pure," rapidly unit testable in isolation, and even could in principle be executed in one's head, because it's the final expression value that is the goal when working in this paradigm. Imperative paradigms on the other hand are not interested as much with expressions and values, but rather statement side-effects, behaviors, and the sequencing together of computations (and it's the concept of sequencing together effectful computations that monads attempt to abstract over). It is the glue code that ties together your pure, effect-free logic and embeds those expressions in a context where they actually have some interaction with computing, hardware, and the outside world; otherwise, they would just be formulae sitting in a spreadsheet with no connection to anything whatsoever. > Attempts can also be made to eliminate IP altogether by providing impure functionality in FP languages by introducing monads for I/O and exceptional behavior, allowing mutation by isolating it in blocks, etc. I believe that makes impure FP languages equivalent to IP, corrupting them and defeating the point of using FP. This point is interesting. One could argue that monads are in fact a way of preserving purity in FP while still attaining effectful imperative-like behavior, since the monad is "just" an AST or a pure value that describes a sequence of computations that ought to take place, and it's up to the runtime to actually interpret this data structure and execute or realize the effects merely described by the monadic value (I suppose an OOP design patternist would see similarities to a "Command pattern" here); however, Conal Elliot has taken this logic to the conclusion that, if it were the case, then the C language must also be "functionally pure." [1] > When often programs can be written much more concisely and clearly by avoiding custom types altogether and focusing on data-driven standard types like numbers, strings and JSON run through transformation functions. An obvious example being how Java programs are often bloated and overengineered because they are object-oriented instead of functional. It's amazing to see how so much boilerplate often contains so little actual business logic. And how languages inspired by Java, like C#, often seem to repeat its shortcomings. Maybe, but there is also a risk of running into the "Primitive Obsession" code smell [2]. If I have a URL, representing that URL as a String now allows malformed URLs or things that are not URLs at all to inhabit that type, reducing the number of static guarantees I can avail myself of; moreover, if I want to extract the scheme, path, etc. from the URL I now have to extract those attributes by way of lower-level text manipulation, substrings, and slices, instead of being able to simply read off those components of the URL from a higher-level representation that actually reifies those components as first-class attributes of a more structured data type. I find that one of the main differences between Haskell and other languages and their ecosystems is the focus on finding good abstractions. Often I have seen Java or C# or golang interfaces two dozen methods wide. Not only does this break "interface segregation principle" and other SOLID dogmas, making it difficult to write other implementors (and often you just end up with the single implementor, at which point the interface barely abstracts over anything at all), such an overspecified interface tends to generalize poorly to other use cases. The more you add to your interface, the more you specify and constrain its structure, the less general it becomes; hence TFA's celebration of monads which, having a minimal complete definition of one operator, can be applied to a shockingly wide variety of domains and are widely relied on by the ecosystem because, as an abstraction only a method wide, monads are subject to much less churn or interface breakage over time. Finding good abstractions is hard, and IMO one of the central problems of writing software. I would summarize the article as observing that in imperative programming, it's possible to proceed naively but expeditiously, papering over the lack of strong and consistent abstractions by just throwing more glue code and flex tape at the problem to paper over any leaks. In Haskell, especially when first designing your types and data structures, the work of abstracting the problem domain adequately is front-loaded and you are forced to think about it up front. [0] https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct... [1] http://conal.net/blog/posts/the-c-language-is-purely-functional http://conal.net/blog/posts/the-c-language-is-purely-functio... [2] https://wiki.c2.com/?PrimitiveObsession https://wiki.c2.com/?PrimitiveObsession

ryandv 2y ago

> I believe that ideally we'd write everything in FP with no IP whatsoever. So no mutable variables, no pass by reference, no iteration. > Then IP would be used to wire up components, similarly to controllers in MVP. This viewpoint was popularized by Gary Bernhardt a while ago as "functional core, imperative shell." [0] Functional paradigms should be used for expressing core logic and transformation of data; code written in this style is side-effect free, "pure," rapidly unit testable in isolation, and even could in principle be executed in one's head, because it's the final expression value that is the goal when working in this paradigm. Imperative paradigms on the other hand are not interested as much with expressions and values, but rather statement side-effects, behaviors, and the sequencing together of computations (and it's the concept of sequencing together effectful computations that monads attempt to abstract over). It is the glue code that ties together your pure, effect-free logic and embeds those expressions in a context where they actually have some interaction with computing, hardware, and the outside world; otherwise, they would just be formulae sitting in a spreadsheet with no connection to anything whatsoever. > Attempts can also be made to eliminate IP altogether by providing impure functionality in FP languages by introducing monads for I/O and exceptional behavior, allowing mutation by isolating it in blocks, etc. I believe that makes impure FP languages equivalent to IP, corrupting them and defeating the point of using FP. This point is interesting. One could argue that monads are in fact a way of preserving purity in FP while still attaining effectful imperative-like behavior, since the monad is "just" an AST or a pure value that describes a sequence of computations that ought to take place, and it's up to the runtime to actually interpret this data structure and execute or realize the effects merely described by the monadic value (I suppose an OOP design patternist would see similarities to a "Command pattern" here); however, Conal Elliot has taken this logic to the conclusion that, if it were the case, then the C language must also be "functionally pure." [1] > When often programs can be written much more concisely and clearly by avoiding custom types altogether and focusing on data-driven standard types like numbers, strings and JSON run through transformation functions. An obvious example being how Java programs are often bloated and overengineered because they are object-oriented instead of functional. It's amazing to see how so much boilerplate often contains so little actual business logic. And how languages inspired by Java, like C#, often seem to repeat its shortcomings. Maybe, but there is also a risk of running into the "Primitive Obsession" code smell [2]. If I have a URL, representing that URL as a String now allows malformed URLs or things that are not URLs at all to inhabit that type, reducing the number of static guarantees I can avail myself of; moreover, if I want to extract the scheme, path, etc. from the URL I now have to extract those attributes by way of lower-level text manipulation, substrings, and slices, instead of being able to simply read off those components of the URL from a higher-level representation that actually reifies those components as first-class attributes of a more structured data type. I find that one of the main differences between Haskell and other languages and their ecosystems is the focus on finding good abstractions. Often I have seen Java or C# or golang interfaces two dozen methods wide. Not only does this break "interface segregation principle" and other SOLID dogmas, making it difficult to write other implementors (and often you just end up with the single implementor, at which point the interface barely abstracts over anything at all), such an overspecified interface tends to generalize poorly to other use cases. The more you add to your interface, the more you specify and constrain its structure, the less general it becomes; hence TFA's celebration of monads which, having a minimal complete definition of one operator, can be applied to a shockingly wide variety of domains and are widely relied on by the ecosystem because, as an abstraction only a method wide, monads are subject to much less churn or interface breakage over time. Finding good abstractions is hard, and IMO one of the central problems of writing software. I would summarize the article as observing that in imperative programming, it's possible to proceed naively but expeditiously, papering over the lack of strong and consistent abstractions by just throwing more glue code and flex tape at the problem to paper over any leaks. In Haskell, especially when first designing your types and data structures, the work of abstracting the problem domain adequately is front-loaded and you are forced to think about it up front. [0] https://www.destroyallsoftware.com/screencasts/catalog/functional-core-imperative-shell https://www.destroyallsoftware.com/screencasts/catalog/funct... [1] http://conal.net/blog/posts/the-c-language-is-purely-functional http://conal.net/blog/posts/the-c-language-is-purely-functio... [2] https://wiki.c2.com/?PrimitiveObsession https://wiki.c2.com/?PrimitiveObsession