5 ms·

I go back and forth on this. On one hand, I _love_ Rust/ML style sum types. They're such a fantastic feature. On the other hand, I wonder how much use they'd ge

by jjice 3y ago

I go back and forth on this. On one hand, I _love_ Rust/ML style sum types. They're such a fantastic feature. On the other hand, I wonder how much use they'd get in a language like Go. If it's introduced, would it radically change the way some problems get solved? Is it that different than an traditional enum (which Go also skirts around)? Pattern matching and exhaustive checks are massive benefits of them though. I guess I'm just oddly conflicted here. I do think that long term, sum types are going to become more prevalent. I'm excited to see it, I'm just interested in how that adoption occurs in existing languages without them.

jchw 3y ago
If I had sum types in Go, I'd use them for state machines and enumerations mostly. I can't see a huge downside; I'm sure some software has little use for it, but it's useful enough for data modelling that protobuf has the sort-of similar oneof primitive. Hmm. On that note, maybe it would be better than nothing to do some kind of code generation here...
jerf 3y ago
I think the answer to your "back and forth" is probably laid out in: https://jerf.org/iri/post/2960/ https://jerf.org/iri/post/2960/ Sum types are useful, even very useful in the right place, but I do think there's a lot of people who use them a couple of times, probably in one of those "right places" and then mistakenly label them in their mind as "better". Just, universally, Platonically "better". They aren't in fact "better"; they're a tool. Sometimes they're the right tool for the job, but much, much more often, they're just a tool that works, and so do several other tools. People who get too excited about sum types need to be sure they square their understanding of how useful they are with the fact that the vast majority of programs are written without them.
- jchw 3y ago
  This article seems almost entirely concerned with code organization, but in my case I basically never do functional programming and am only concerned about data modelling and data structures. In an adjacent, comment I do acknowledge one point (probably not all software really needs sum types) but I still feel as though languages without sum types are missing an important data and state modelling tool. Trying to take something like a state machine and jam it into interfaces or polymorphism kind of sucks; you lose exhaustiveness checking obviously, but also it enforces a lot of constraints about control flow and data. In Go parlance, if each of my states has a method with its receiver set to the state type, then I can only access that data, so for example I'd need to pass something in or out to handle state transitions. Not ideal IMO. I feel this pain basically any time I hand-write lexical scanners/parsers in Go or even C++.
  - masklinn 3y ago
    > I still feel as though languages without sum types are missing an important data and state modelling tool. That's because they are. jerf subtly shifts the point to one they can criticise, but it does not change the basic fact that sum types are a critical tool which is just... missing. There's probably no tool which can't be misused, even the humble boolean, that's not an issue with the tool, and pointing that out is at best irrelevant. It does not change the fact of the matter: you're missing a critical axis of composition. It's like saying screwdrivers are useful but you can misuse them to hammer nails as if that justified trying to screw with a hammer.
    - jerf 3y ago
      Where I'd disagree is that they are a tool, not a critical tool, and they aren't missing from Go, they are simply not the preferred choice. You can cover 75% of the use cases with this approach. It is not 100% of the use cases. But there isn't a language where you can cover 100% of the use cases with 100% effectiveness, which is why we don't have and never will have The One True Language. Moreover, Go seems to attract this sort of criticism as if Go is Uniquely Broken and it's nirvana in all the other languages... but I've used enough of them to know better. Sum types are great, until you hit the branch of the expression problem where you really need the other side, and if you're in a language that favors them, you're going to get the same 75% experience, just mirror imaged.
      - nicoburns 3y ago
        > Sum types are great, until you hit the branch of the expression problem where you really need the other side, and if you're in a language that favors them, you're going to get the same 75% experience, just mirror imaged. Which other side? Product types (aka structs)? I don't think there are any languages with Sum types that don't also include Product types.
      - deleted 3y ago
        [deleted]
  - jerf 3y ago
- avgcorrection 3y ago
  I like how you start the article by deriding this idea of using sum types dogmatically because “FP is Better” (the dogmatic capital-case “Better”, even) and then close the article with a therapeutic angle about making do with what you are given. > I don't really care if you do or do not stay angry at the language you're forced to work in for your job. What I do want for you is to be able to make the best of the situation you're in and not be unhappy. Because maybe enumerations in Go are subpar compared to other languages (FP or not).
- bobbylarrybobby 3y ago
  It's not the tool that's better; it's having the tool that's better.
- schrodingerscow 3y ago
  I guess what I don’t understand about this is sum types represent a state that is so ubiquitous in our lives that it’s hard for me to go a day without seeing one. It’s simply the state of something either is this or that or that. It would be like a language without records. It’s missing a part of reality that shows up all the time
Zach_the_Lizard 3y ago
Sum types with pattern matching would likely take the place of (foo, error) in a lot of codebases. This is especially true in cases where a function returns a collection of results where each result is independent from other results and a result can succeed or fail. For instance, a batch report generator that is called every $INTERVAL might return a ([]Report metadata, error) today, but each report could have succeeded or failed without impacting the others. The output is emailed to $SOMEONE to let them know the reports ran and information about each. In today's world, the "error" could be a special error type that capture failures on a per report basis. The ReportMetadata type could also have an Error field, but one is not forced to check either. Sum types could force checking for error on a per report basis, increasing the odds something is done with the error.

by jjice 3y ago

jchw 3y ago

If I had sum types in Go, I'd use them for state machines and enumerations mostly. I can't see a huge downside; I'm sure some software has little use for it, but it's useful enough for data modelling that protobuf has the sort-of similar oneof primitive. Hmm. On that note, maybe it would be better than nothing to do some kind of code generation here...

jerf 3y ago

I think the answer to your "back and forth" is probably laid out in: https://jerf.org/iri/post/2960/ https://jerf.org/iri/post/2960/ Sum types are useful, even very useful in the right place, but I do think there's a lot of people who use them a couple of times, probably in one of those "right places" and then mistakenly label them in their mind as "better". Just, universally, Platonically "better". They aren't in fact "better"; they're a tool. Sometimes they're the right tool for the job, but much, much more often, they're just a tool that works, and so do several other tools. People who get too excited about sum types need to be sure they square their understanding of how useful they are with the fact that the vast majority of programs are written without them.

jchw 3y ago
This article seems almost entirely concerned with code organization, but in my case I basically never do functional programming and am only concerned about data modelling and data structures. In an adjacent, comment I do acknowledge one point (probably not all software really needs sum types) but I still feel as though languages without sum types are missing an important data and state modelling tool. Trying to take something like a state machine and jam it into interfaces or polymorphism kind of sucks; you lose exhaustiveness checking obviously, but also it enforces a lot of constraints about control flow and data. In Go parlance, if each of my states has a method with its receiver set to the state type, then I can only access that data, so for example I'd need to pass something in or out to handle state transitions. Not ideal IMO. I feel this pain basically any time I hand-write lexical scanners/parsers in Go or even C++.
- masklinn 3y ago
  > I still feel as though languages without sum types are missing an important data and state modelling tool. That's because they are. jerf subtly shifts the point to one they can criticise, but it does not change the basic fact that sum types are a critical tool which is just... missing. There's probably no tool which can't be misused, even the humble boolean, that's not an issue with the tool, and pointing that out is at best irrelevant. It does not change the fact of the matter: you're missing a critical axis of composition. It's like saying screwdrivers are useful but you can misuse them to hammer nails as if that justified trying to screw with a hammer.
  - jerf 3y ago
    Where I'd disagree is that they are a tool, not a critical tool, and they aren't missing from Go, they are simply not the preferred choice. You can cover 75% of the use cases with this approach. It is not 100% of the use cases. But there isn't a language where you can cover 100% of the use cases with 100% effectiveness, which is why we don't have and never will have The One True Language. Moreover, Go seems to attract this sort of criticism as if Go is Uniquely Broken and it's nirvana in all the other languages... but I've used enough of them to know better. Sum types are great, until you hit the branch of the expression problem where you really need the other side, and if you're in a language that favors them, you're going to get the same 75% experience, just mirror imaged.
    - nicoburns 3y ago
      > Sum types are great, until you hit the branch of the expression problem where you really need the other side, and if you're in a language that favors them, you're going to get the same 75% experience, just mirror imaged. Which other side? Product types (aka structs)? I don't think there are any languages with Sum types that don't also include Product types.
    - deleted 3y ago
      [deleted]
- jerf 3y ago
avgcorrection 3y ago
I like how you start the article by deriding this idea of using sum types dogmatically because “FP is Better” (the dogmatic capital-case “Better”, even) and then close the article with a therapeutic angle about making do with what you are given. > I don't really care if you do or do not stay angry at the language you're forced to work in for your job. What I do want for you is to be able to make the best of the situation you're in and not be unhappy. Because maybe enumerations in Go are subpar compared to other languages (FP or not).
bobbylarrybobby 3y ago
It's not the tool that's better; it's having the tool that's better.
schrodingerscow 3y ago
I guess what I don’t understand about this is sum types represent a state that is so ubiquitous in our lives that it’s hard for me to go a day without seeing one. It’s simply the state of something either is this or that or that. It would be like a language without records. It’s missing a part of reality that shows up all the time

Zach_the_Lizard 3y ago

Sum types with pattern matching would likely take the place of (foo, error) in a lot of codebases. This is especially true in cases where a function returns a collection of results where each result is independent from other results and a result can succeed or fail. For instance, a batch report generator that is called every $INTERVAL might return a ([]Report metadata, error) today, but each report could have succeeded or failed without impacting the others. The output is emailed to $SOMEONE to let them know the reports ran and information about each. In today's world, the "error" could be a special error type that capture failures on a per report basis. The ReportMetadata type could also have an Error field, but one is not forced to check either. Sum types could force checking for error on a per report basis, increasing the odds something is done with the error.