Comments (17)
piaste
commented on May 15, 2024
1
I too vote 2. As I mentioned, we use this type inference every single time we make a database query, and we cannot add a type annotation because the type is generated by the type provider and doesn't have a usable name.
On the other side, the issue #86 (that the Bind in #87 resolved) only appears in a couple of spots through our codebase, and a workaround should be possible, since all CEs are just sugar, although it seems a bit tricky.
For reference, take this piece of v1.2.6 code:
let f () = asyncResult { return "" }
let g () =
asyncResult {
let! r1 = f ()
let! (r2 : Result<string, _>) = f ()
return (r2 = Ok r1)
}
Not sure how this could be done in v1.4.0 without forsaking the use of asyncResult entirely.
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
Ugh this feels like a potential compiler bug. cc @cartermp @baronfel. This seems to only happen when using the Source members.
A less verbose work around is to add a type annotation to v
let f () = asyncResult {
let! (v : X) = async { return X() }
return v.A
}Additionally this problem is not apparent when using the <LangVersion>preview</LangVersion> in the fsproj.
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
With all these breaking changes (#84 #85) I should probably unlist these newest packages and bump this package to v2.
from fstoolkit.errorhandling.
baronfel
commented on May 15, 2024
Preview opts you into applicative support, are you thinking there's an interaction there with typechecking?
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
If I expand the example to:
let f () = asyncResult {
let! v = async { return X() }
let! x = async { return X() }
let! y = async { return X() }
return v.A, x.A, y.A
}This no longer works because it's not in applicative mode. So there's an issue with type inference with regards to Source members and Classes/Anonymous Records
from fstoolkit.errorhandling.
cartermp
commented on May 15, 2024
This looks like a compiler regression given that it doesn't repro unless you turn on preview, which actives applicatives and the associating typechecking.
from fstoolkit.errorhandling.
baronfel
commented on May 15, 2024
That's not how I read it, @cartermp. In #88 (comment) @TheAngryByrd said that turning on preview fixed the initial report, which suggest to me that the rewrite to BindReturn that happened works as expected. The first example is a pretty classic BindReturn scenario.
The example in #88 (comment) isn't something that's easily transformable to BindReturn, etc, so it surfaces the original issue even in an environment with langversion:preview enabled. I've replicated this behavior in a sample project for verification and I'm certain I don't have preview enabled.
from fstoolkit.errorhandling.
cartermp
commented on May 15, 2024
Oh, derp. I misread
from fstoolkit.errorhandling.
baronfel
commented on May 15, 2024
here's the code I'm tinkering around with to show the difference between how classes are resolved vs how records are resolved:
[<Sealed>]
type X() =
member _.A = 1
type Y = { A : int }
let f () = asyncResult {
let! a = async { return X() }
let! b = async { return X() }
let! c = async { return X() }
return a.A, b.A, c.A
}
let g () = asyncResult {
let! a = async { return { A = 1 } }
let! b = async { return { A = 1 } }
let! c = async { return { A = 1 } }
return a.A, b.A, c.A
}each of the let! in the f() are throwing the following error:
error FS0041: No overloads match for method 'Bind'.
Known types of arguments: Async<Result<X,'a>> * (Y -> Async<Result<(int * int * int),'b>>)
Available overloads:
- member AsyncResultBuilder.Bind : asyncComputation:Async<'T> * binder:('T -> Async<Result<'U,'TError>>) -> Async<Result<'U,'TError>> // Argument 'binder' doesn't match
- member AsyncResultBuilder.Bind : asyncComputation:System.Threading.Tasks.Task<'T> * binder:('T -> Async<Result<'U,'TError>>) -> Async<Result<'U,'TError>> // Argument 'asyncComputation' doesn't match
- member AsyncResultBuilder.Bind : asyncResult:Async<Result<'T,'TError>> * binder:('T -> Async<Result<'U,'TError>>) -> Async<Result<'U,'TError>> // Argument 'binder' doesn't match
which to me looks like we're definitely mis-computing the type of the binder argument for classes somehow?
from fstoolkit.errorhandling.
baronfel
commented on May 15, 2024
more findings:
@TheAngryByrd and I added some logging to the CE typecheck pass and went through an exercise of manually translating the logged SynExprs we saw into the actual builder calls.
Final Delay call emitted by the compiler
SynExpr.Lambda
(false, false,
SynSimplePats.SimplePats
([SynSimplePat.Id
(unitVar, None, true, false, false,
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true)],
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true),
SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@, unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots ([Bind], []),
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Tuple
(false,
[SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@, unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots ([Source], []),
/Users/chethusk/oss/scratch/source/Library.fs (11,11--11,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Paren
(SynExpr.App
(NonAtomic, false, SynExpr.Ident async,
SynExpr.CompExpr
(false, { contents = false },
SynExpr.YieldOrReturn
((false, true),
SynExpr.App
(Atomic, false, SynExpr.Ident X,
SynExpr.Const
(SynConst.Unit,
/Users/chethusk/oss/scratch/source/Library.fs (11,27--11,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (11,26--11,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (11,19--11,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (11,17--11,31) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (11,11--11,31) IsSynthetic=false),
unknown (1,0--1,0) IsSynthetic=false, None,
/Users/chethusk/oss/scratch/source/Library.fs (11,11--11,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false, None,
/Users/chethusk/oss/scratch/source/Library.fs (11,11--11,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (11,11--11,31) IsSynthetic=true);
SynExpr.MatchLambda
(false,
/Users/chethusk/oss/scratch/source/Library.fs (11,7--11,8) IsSynthetic=false,
[Clause
(SynPat.Named
(SynPat.Wild
/Users/chethusk/oss/scratch/source/Library.fs (11,7--11,8) IsSynthetic=false,
a, false, None,
/Users/chethusk/oss/scratch/source/Library.fs (11,7--11,8) IsSynthetic=false),
None,
SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@,
unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots ([Bind], []),
/Users/chethusk/oss/scratch/source/Library.fs (12,2--12,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Tuple
(false,
[SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@,
unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots ([Source], []),
/Users/chethusk/oss/scratch/source/Library.fs (12,11--12,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Paren
(SynExpr.App
(NonAtomic, false, SynExpr.Ident async,
SynExpr.CompExpr
(false, { contents = false },
SynExpr.YieldOrReturn
((false, true),
SynExpr.App
(Atomic, false,
SynExpr.Ident X,
SynExpr.Const
(SynConst.Unit,
/Users/chethusk/oss/scratch/source/Library.fs (12,27--12,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (12,26--12,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (12,19--12,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (12,17--12,31) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (12,11--12,31) IsSynthetic=false),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (12,11--12,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false, None,
/Users/chethusk/oss/scratch/source/Library.fs (12,11--12,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (12,11--12,31) IsSynthetic=true);
SynExpr.MatchLambda
(false,
/Users/chethusk/oss/scratch/source/Library.fs (12,7--12,8) IsSynthetic=false,
[Clause
(SynPat.Named
(SynPat.Wild
/Users/chethusk/oss/scratch/source/Library.fs (12,7--12,8) IsSynthetic=false,
b, false, None,
/Users/chethusk/oss/scratch/source/Library.fs (12,7--12,8) IsSynthetic=false),
None,
SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@,
unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots ([Bind], []),
/Users/chethusk/oss/scratch/source/Library.fs (13,2--13,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Tuple
(false,
[SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident builder@,
unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots
([Source], []),
/Users/chethusk/oss/scratch/source/Library.fs (13,11--13,31) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Paren
(SynExpr.App
(NonAtomic, false,
SynExpr.Ident async,
SynExpr.CompExpr
(false,
{ contents =
false },
SynExpr.YieldOrReturn
((false, true),
SynExpr.App
(Atomic,
false,
SynExpr.Ident
X,
SynExpr.Const
(SynConst.Unit,
/Users/chethusk/oss/scratch/source/Library.fs (13,27--13,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (13,26--13,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (13,19--13,29) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (13,17--13,31) IsSynthetic=false),
/Users/chethusk/oss/scratch/source/Library.fs (13,11--13,31) IsSynthetic=false),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (13,11--13,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (13,11--13,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (13,11--13,31) IsSynthetic=true);
SynExpr.MatchLambda
(false,
/Users/chethusk/oss/scratch/source/Library.fs (13,7--13,8) IsSynthetic=false,
[Clause
(SynPat.Named
(SynPat.Wild
/Users/chethusk/oss/scratch/source/Library.fs (13,7--13,8) IsSynthetic=false,
c, false, None,
/Users/chethusk/oss/scratch/source/Library.fs (13,7--13,8) IsSynthetic=false),
None,
SynExpr.App
(NonAtomic, false,
SynExpr.DotGet
(SynExpr.Ident
builder@,
unknown (1,0--1,0) IsSynthetic=false,
LongIdentWithDots
([Return], []),
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=true),
SynExpr.Paren
(SynExpr.Paren
(SynExpr.Tuple
(false,
[SynExpr.LongIdent
(false,
LongIdentWithDots
([a; A],
[/Users/chethusk/oss/scratch/source/Library.fs (14,10--14,11) IsSynthetic=false]),
None,
/Users/chethusk/oss/scratch/source/Library.fs (14,9--14,12) IsSynthetic=false);
SynExpr.LongIdent
(false,
LongIdentWithDots
([b; A],
[/Users/chethusk/oss/scratch/source/Library.fs (14,15--14,16) IsSynthetic=false]),
None,
/Users/chethusk/oss/scratch/source/Library.fs (14,14--14,17) IsSynthetic=false);
SynExpr.LongIdent
(false,
LongIdentWithDots
([c; A],
[/Users/chethusk/oss/scratch/source/Library.fs (14,20--14,21) IsSynthetic=false]),
None,
/Users/chethusk/oss/scratch/source/Library.fs (14,19--14,22) IsSynthetic=false)],
[/Users/chethusk/oss/scratch/source/Library.fs (14,12--14,13) IsSynthetic=false;
/Users/chethusk/oss/scratch/source/Library.fs (14,17--14,18) IsSynthetic=false],
/Users/chethusk/oss/scratch/source/Library.fs (14,9--14,22) IsSynthetic=false),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=false,
DebugPointForTarget.Yes)],
DebugPointAtBinding
/Users/chethusk/oss/scratch/source/Library.fs (13,2--13,31) IsSynthetic=false,
/Users/chethusk/oss/scratch/source/Library.fs (14,2--14,22) IsSynthetic=false)],
[],
/Users/chethusk/oss/scratch/source/Library.fs (13,2--13,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false,
None,
/Users/chethusk/oss/scratch/source/Library.fs (13,2--13,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (13,2--13,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (13,2--14,22) IsSynthetic=false,
DebugPointForTarget.Yes)],
DebugPointAtBinding
/Users/chethusk/oss/scratch/source/Library.fs (12,2--12,31) IsSynthetic=false,
/Users/chethusk/oss/scratch/source/Library.fs (13,2--14,22) IsSynthetic=false)],
[],
/Users/chethusk/oss/scratch/source/Library.fs (12,2--12,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false, None,
/Users/chethusk/oss/scratch/source/Library.fs (12,2--12,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (12,2--12,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (12,2--14,22) IsSynthetic=false,
DebugPointForTarget.Yes)],
DebugPointAtBinding
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=false,
/Users/chethusk/oss/scratch/source/Library.fs (12,2--14,22) IsSynthetic=false)],
[],
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true),
unknown (1,0--1,0) IsSynthetic=false, None,
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true),
/Users/chethusk/oss/scratch/source/Library.fs (11,2--11,31) IsSynthetic=true)]
expanded equivalent
asyncResult.Delay(fun () ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun a ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun b ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun c ->
asyncResult.Return((a.A, b.A, c.A))
))
))
))
)As best as we can tell, the emitted lambdas are correct in terms of shape. However, when we test this by manually entering this expansion into a library file with the X type defined, we see that the compiler still complains about being unable to resolve the type based on usage:
open FsToolkit.ErrorHandling
type X() =
member _.A = 1
let thing =
asyncResult.Delay(fun () ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun a ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun b ->
asyncResult.Bind(asyncResult.Source((async { return X() })), (fun c ->
asyncResult.Return((a.A, b.A, c.A)) // here you get ambigiuous lookup errors on each usage of `.A`
))
))
))
)we did notice that if the lambdas were explicitly typed (as is what would happen if the let! was explicitly typed (let! (a: X) = async { return X() })), the desugared form compiles well.
So perhaps there's some more general type-inference problem at play here @cartermp?
from fstoolkit.errorhandling.
baronfel
commented on May 15, 2024
This seems to be because of the presence of the Bind(Async<'t>, 't -> Async<Result<'t, 'err>>) overload. This was just introduced in version 1.4.1 of this library, to allow users to unwrap only one level of the Async<Result<'t, 'err>> wrapped type. However it seems that adding these bind overloads makes the compiler unhappy. The ambiguity can be solved by forcing explicit type patterns (let! (a: X)) at each callsite, giving users the choice of which 'layers' they want to unwrap, but that's a huge burden to add.
This seems like a huge use case for the 'restraint' concept that @TheAngryByrd likes to talk about:
member _.Bind(a: Async<'t>, binder: 't -> Async<Result<'t, 'err>>) when 't is not Result<blah, blah> = ...from fstoolkit.errorhandling.
sandeep-eroad
commented on May 15, 2024
I am also seeing similar behaviour with Postgres Type provider https://github.com/demetrixbio/FSharp.Data.Npgsql with latest version of FsToolkit but this works fine with version 1.2.2.
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
Well the current options are:
- See if there's a way to get the F# compiler to fix this problem (seems unlikely)
- Remove the
Bindintroduced in #87 to allow for type inference to work properly and list work arounds for handling the other wrapper type. - Keep the
Bindfrom #87 and have this as a known issue in documentation where you have to add a type annotation for classes.
from fstoolkit.errorhandling.
sandeep-eroad
commented on May 15, 2024
I vote for 2 option.
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
On the other side, the issue #86 (that the Bind in #87 resolved) only appears in a couple of spots through our codebase, and a workaround should be possible, since all CEs are just sugar, although it seems a bit tricky.
Yeah this was the same for one of my work projects, but there was no real good reason for us to be doing it.
Ok I'm going to revert #87 and yank the release of 1.4.1 for now.
from fstoolkit.errorhandling.
TheAngryByrd
commented on May 15, 2024
@piaste so typically if I needed the Result directly for some reason, I would just use an async CE.
We also might be missing other function helpers but the most basic to just handle either Ok or Error cases,
FsToolkit.ErrorHandling/src/FsToolkit.ErrorHandling/AsyncResult.fs
Lines 23 to 24 in aa9f8ad
tends to be able to handle all cases I've come across.
from fstoolkit.errorhandling.
piaste
commented on May 15, 2024
@TheAngryByrd the issue happened when we had a long taskResult computation, as usually every API endpoint is a single taskResult CE, but at one particular point in the flow we had an error return that we were able to handle on the spot instead of returning a HTTP failure. Restructuring the entire CE to be a plain async with manual error handling would not be worth it.
For now, I've solved it somewhat clumsily by running the right side of the unwrapping throgh Task.map (function | Ok x -> Choice1Of2 x | Error y -> Choice2Of2 y), so the Choice doesn't get unwrapped and it can be handled manually.
from fstoolkit.errorhandling.
Related Issues (20)
- F# 6 task CE support (instead of Ply) HOT 1
- Task to AsyncResult transition wraps `Exception` into the `AggregateException` HOT 8
- Seq.sequenceResultM returns a list instead of a seq HOT 1
- TaskResult.ofTask? HOT 2
- Use ListCollector on List operations to improve perf HOT 4
- List.traverseValidationA' should be private? HOT 1
- Add explicit type parameters to ignore functions HOT 5
- Move TaskResult (and friends) to core FsToolkit.ErrorHandling package HOT 9
- TaskResultCE breaks with a bind in branching such as if HOT 2
- List.traverseResultA and friends have x @ y on the error branch, this could potentially blow up HOT 5
- Add Option.maybe
- Task wrapped result + option helpers HOT 1
- Worried about the Diamond dependency problem HOT 6
- Documentation for Validation operators mentions Bind (>>=), but the library doesn't implement it HOT 1
- Should List.sequenceValidationA preserve order? HOT 2
- FSharp.Core version warning (net7.0) HOT 14
- Make Result.defaultWith accept error, or remove it HOT 2
- Overload issues with TaskResult on generic functions HOT 2
- Add Option.ofPair HOT 5
- Add asyncValidation CE, or make asyncResult (and result?) CEs work with 'and!' HOT 4
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from fstoolkit.errorhandling.