4 ms·

Either is nearly in the language anyways. The vast majority of pragmatic go functions will return [Result, Error] and or just [Error]. We are only missing suppo

Either is nearly in the language anyways. The vast majority of pragmatic go functions will return [Result, Error] and or just [Error]. We are only missing support to treat this as a monad.

corethree 3y ago
You don't need support. Monad composition isn't a special feature it can be implemented directly. Not an expert in Go but I think you can do this: func compose[A any, B any, C any](a func(A) (B, error), b func(B) (C, error)) func(A) (C, error) { return func(aInp A) (C, error) { res, err := a(aInp) if err == nil { return b(res) } else { return *new(C), err } } } The above is equivalent to haskells fish operator >=> The bind operator (>>=) can be implimented in terms of composition: func bind[A any, B any, C any](a func(A) (B, error), b func(B) (C, error), aInput A) (C, error) { return compose[A, B, C](a, b)(aInput) }
kadoban 3y ago
Either as a pattern is _used_ everywhere, but the standard library in go doesn't have one (people just use a tuple), so it's _always_ encoded wrong. It's very annoying.
- corethree 3y ago
  There is no tuple type in go. When you see a func() (A, error) that is not a function returning a tuple. It is a function returning two values that cannot be composed. You can't A(B()) if B returns two values. It's pure comedy.
  - deleted 3y ago
    [deleted]
  - duskwuff 3y ago
    > You can't A(B()) if B returns two values. You can if A is a function which takes two arguments, e.g. package main import "log" func A(x, y int) { log.Printf("%d, %d", x, y) } func B() (int, int) { return 1, 2 } func main() { A(B()) } https://go.dev/play/p/Jp4B0L6NJj2 https://go.dev/play/p/Jp4B0L6NJj2
    - erik_seaberg 3y ago
      What you can't do is a(b(), c()) unless b and c return single values. And there are no slices or channels of tuples, return values must be destructured right away.
      - deleted 3y ago
        [deleted]
eweise 3y ago
To me, the problem is that Go returns two values which makes it hard to compose functions.
- sambeau 3y ago
  That's deliberate to stop you trying to compose functions that return errors. You should be explicitly handling the errors before you compose.
  - eweise 3y ago
    great, except 99% of the time I want to handle the error by bubbling it up to a top level routine. From my experience, "handling" the error means wrapping it in another error and returning, which is what you get from other languages for free.

Either is nearly in the language anyways. The vast majority of pragmatic go functions will return [Result, Error] and or just [Error]. We are only missing support to treat this as a monad.

corethree 3y ago

You don't need support. Monad composition isn't a special feature it can be implemented directly. Not an expert in Go but I think you can do this: func compose[A any, B any, C any](a func(A) (B, error), b func(B) (C, error)) func(A) (C, error) { return func(aInp A) (C, error) { res, err := a(aInp) if err == nil { return b(res) } else { return *new(C), err } } } The above is equivalent to haskells fish operator >=> The bind operator (>>=) can be implimented in terms of composition: func bind[A any, B any, C any](a func(A) (B, error), b func(B) (C, error), aInput A) (C, error) { return compose[A, B, C](a, b)(aInput) }

kadoban 3y ago

Either as a pattern is _used_ everywhere, but the standard library in go doesn't have one (people just use a tuple), so it's _always_ encoded wrong. It's very annoying.

corethree 3y ago
There is no tuple type in go. When you see a func() (A, error) that is not a function returning a tuple. It is a function returning two values that cannot be composed. You can't A(B()) if B returns two values. It's pure comedy.
- deleted 3y ago
  [deleted]
- duskwuff 3y ago
  > You can't A(B()) if B returns two values. You can if A is a function which takes two arguments, e.g. package main import "log" func A(x, y int) { log.Printf("%d, %d", x, y) } func B() (int, int) { return 1, 2 } func main() { A(B()) } https://go.dev/play/p/Jp4B0L6NJj2 https://go.dev/play/p/Jp4B0L6NJj2
  - erik_seaberg 3y ago
    What you can't do is a(b(), c()) unless b and c return single values. And there are no slices or channels of tuples, return values must be destructured right away.
    - deleted 3y ago
      [deleted]

eweise 3y ago

To me, the problem is that Go returns two values which makes it hard to compose functions.

sambeau 3y ago
That's deliberate to stop you trying to compose functions that return errors. You should be explicitly handling the errors before you compose.
- eweise 3y ago
  great, except 99% of the time I want to handle the error by bubbling it up to a top level routine. From my experience, "handling" the error means wrapping it in another error and returning, which is what you get from other languages for free.