Re: [swift-evolution] [Pitch] Guarding on enum values

[Kevin Ballard via swift-evolution]

You actually can do simple let-bindings in if-let and guard-let via the `case 
let` syntax:

guard case let r = returnsResult(), case let .Succeed(m) = r else { ... }

Although the problem with this is `r` still isn't visible inside of the else 
block, because it's part of the guard statement and none of the bound 
identifiers are visible inside of the else. But this really ends up being the 
equivalent of

let r = returnsResult()
guard case let .Succeed(m) = r else { return r }

anyway so I don't really see the point in pursuing this.

As for changing if-let and guard-let by default to do this style of matching, I 
believe the Swift team did consider doing that, but the overwhelming prevalence 
of Optionals in Swift is why they didn't go ahead with it. I bet if you examine 
your own code you'll find that normal if-let and guard-lets outweigh if-case 
and guard-case by a very large amount.

-Kevin

On Sun, Dec 27, 2015, at 08:25 AM, Thorsten Seitz via swift-evolution wrote:
> The problem is that currently the if-let and guard-let syntax is reserved for 
> unwrapping optionals and therefore cannot be used (at least not 
> unambiguously) for simple let-bindings as well, which is required here.
> 
> My example therefore needs the following change (sorry, I did not make this 
> explicit):
> 
> 1. allow let-bindings in if- and guard-statements and
> 2. require explicit optional unwrapping by pattern matching in if- and 
> guard-statements
> 
> In addition I’d like to add the following (but that’s really a separate 
> proposal):
> 3. drop the „case“ keyword for pattern matching
> 
> The example would then look like follows (written in multiple lines for 
> adding comments):
> 
> guard 
>  let r = returnsResult(), // simple let-binding
>  let .Succeed(m) = r  // pattern matching
> else {
>  return r 
> }
> 
> Unwrapping optionals would then look like follows (i.e. no special syntax for 
> unwrapping optionals):
> 
> if let .Some(x) = x {
>   …
> }
> 
> A shorter alternative might be: if let x ?= x { … }
> 
> IIRC this or something similar was part of an earlier Swift release and was 
> streamlined to the current syntax because optionals are quite common and 
> already have special syntax sugar. The problem is that the current syntax 
> while being convenient for its succinctness is ambiguous with simple 
> let-bindings which is inconsistent and - more importantly - makes extending 
> if-statements and guard-statements by simple let-bindings impossible.
> 
> -Thorsten
> 
> 
> > Am 24.12.2015 um 18:13 schrieb Félix Cloutier :
> > 
> > Wait, no, there's a problem with that. You can't use `r` in the guard scope 
> > because `returnsResult()` might not have succeeded.
> > 
> > Félix
> > 
> >> Le 24 déc. 2015 à 09:37:36, Félix Cloutier via swift-evolution 
> >>  a écrit :
> >> 
> >> I like that it's consistent with the if syntax (even though I don't really 
> >> like the if syntax) and that there's no dangling parts after the else.
> >> 
> >> Félix
> >> 
> >>> Le 24 déc. 2015 à 06:29:17, Thorsten Seitz via swift-evolution 
> >>>  a écrit :
> >>> 
> >>> What do you think of
> >>> 
> >>> guard let r = returnsResult(), case let .Succeed(m) = r else {
> >>>  return r 
> >>> }
> >>> 
> >>> Which binds r only within the scope of the guard as desired.
> >>> 
> >>> Written in multiple lines
> >>> 
> >>> guard 
> >>>  let r = returnsResult(), 
> >>>  case let .Succeed(m) = r 
> >>> else {
> >>>  return r 
> >>> }
> >>> 
> >>> -Thorsten 
> >>> 
>  Am 24.12.2015 um 01:02 schrieb Andrew Duncan via swift-evolution 
>  :
>  
>  Yes, which would revert to Brent’s suggestion. But you have generalized 
>  it in a very compatible way.
>  
>  As I read somewhere, improving programming languages comes from removing 
>  limitations rather than adding features. I intend for this Pitch to be 
>  the former, although it does kind of look like the latter.
>  
> > On 23 Dec, 2015, at 15:58, Joe Groff  wrote:
> > 
> > 
> >> On Dec 23, 2015, at 3:56 PM, Andrew Duncan  
> >> wrote:
> >> 
> >> More progress! This sounds good, but it looks like what you intend is 
> >> for r to be the error message in the Result enum type.
> >> 
> >> enum Result {
> >> case .Fail(String)// Error message
> >> case .Succeed(MyType) // Something to work with
> >> }
> >> 
> >> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) 
> >> {
> >> return r // Looks like r is bound to the error String. 
> >>  // But maybe you meant r = the entire returnsResult() result.
> >> }
> > 
> > I see. If it's an arbitrary pattern, you can match 'case let r' to bind 
> > the entire value instead of picking out the payload of the other case. 

Re: [swift-evolution] [Pitch] Guarding on enum values

[Thorsten Seitz via swift-evolution]

> Am 28.12.2015 um 02:31 schrieb Kevin Ballard via swift-evolution 
> :
> 
> You actually can do simple let-bindings in if-let and guard-let via the `case 
> let` syntax:
> 
> guard case let r = returnsResult(), case let .Succeed(m) = r else { ... }
> 
> Although the problem with this is `r` still isn't visible inside of the else 
> block, because it's part of the guard statement and none of the bound 
> identifiers are visible inside of the else.

Which is correct because "case let" can fail as it is not a simple let-binding 
but pattn matching. That's why a real simple let-binding might be attractive to 
have. Names bound by these (or rather by let-bindings that happen before a 
failable binding like pattern matching or optionla unwrapping) should be 
available in the else block.

> But this really ends up being the equivalent of
> 
> let r = returnsResult()
> guard case let .Succeed(m) = r else { return r }
> 
> anyway so I don't really see the point in pursuing this.

The point was about keeping the scope of "r" restricted to the guard clause.
This might not be worth the effort, of course.

> As for changing if-let and guard-let by default to do this style of matching, 
> I believe the Swift team did consider doing that, but the overwhelming 
> prevalence of Optionals in Swift is why they didn't go ahead with it. I bet 
> if you examine your own code you'll find that normal if-let and guard-lets 
> outweigh if-case and guard-case by a very large amount.

I agree without having to examine my code but I'm still unsure whether it 
wouldn't be better to unify let bindings with pattern matching while 
disambiguating simple bindings from pattern matching and optional unwrapping as 
special case of pattern matching:

let pattern = expression 

If "pattern" is a simple variable the pattern matching cannot fail, so we have 
a simple let-binding. Using this in an if- or guard-statement would make the 
bound name available in the statement block(s) unless a failable pattern 
matching came before it.

For syntactically light optional unwrapping "expression" can be "x?", i.e. "if 
let x = x? {...}".
This syntax sugar would be in line with optional chaining, like "x?.property = 
42" where we can understand "x?" to mean the unwrapped optional if present and 
otherwise skipping the statement.

-Thorsten 

> 
> -Kevin
> 
>> On Sun, Dec 27, 2015, at 08:25 AM, Thorsten Seitz via swift-evolution wrote:
>> The problem is that currently the if-let and guard-let syntax is reserved 
>> for unwrapping optionals and therefore cannot be used (at least not 
>> unambiguously) for simple let-bindings as well, which is required here.
>> 
>> My example therefore needs the following change (sorry, I did not make this 
>> explicit):
>> 
>> 1. allow let-bindings in if- and guard-statements and
>> 2. require explicit optional unwrapping by pattern matching in if- and 
>> guard-statements
>> 
>> In addition I’d like to add the following (but that’s really a separate 
>> proposal):
>> 3. drop the „case“ keyword for pattern matching
>> 
>> The example would then look like follows (written in multiple lines for 
>> adding comments):
>> 
>> guard 
>> let r = returnsResult(),// simple let-binding
>> let .Succeed(m) = r  // pattern matching
>> else {
>> return r 
>> }
>> 
>> Unwrapping optionals would then look like follows (i.e. no special syntax 
>> for unwrapping optionals):
>> 
>> if let .Some(x) = x {
>>…
>> }
>> 
>> A shorter alternative might be: if let x ?= x { … }
>> 
>> IIRC this or something similar was part of an earlier Swift release and was 
>> streamlined to the current syntax because optionals are quite common and 
>> already have special syntax sugar. The problem is that the current syntax 
>> while being convenient for its succinctness is ambiguous with simple 
>> let-bindings which is inconsistent and - more importantly - makes extending 
>> if-statements and guard-statements by simple let-bindings impossible.
>> 
>> -Thorsten
>> 
>> 
>>> Am 24.12.2015 um 18:13 schrieb Félix Cloutier :
>>> 
>>> Wait, no, there's a problem with that. You can't use `r` in the guard scope 
>>> because `returnsResult()` might not have succeeded.
>>> 
>>> Félix
>>> 
 Le 24 déc. 2015 à 09:37:36, Félix Cloutier via swift-evolution 
  a écrit :
 
 I like that it's consistent with the if syntax (even though I don't really 
 like the if syntax) and that there's no dangling parts after the else.
 
 Félix
 
> Le 24 déc. 2015 à 06:29:17, Thorsten Seitz via swift-evolution 
>  a écrit :
> 
> What do you think of
> 
> guard let r = returnsResult(), case let .Succeed(m) = r else {
> return r 
> }
> 
> Which binds r only within the scope of the guard as desired.
> 
> Written in multiple lines
> 
> guard 
> let r = returnsResult(), 

Re: [swift-evolution] [Pitch] Guarding on enum values

[Félix Cloutier via swift-evolution]

Wait, no, there's a problem with that. You can't use `r` in the guard scope 
because `returnsResult()` might not have succeeded.

Félix

> Le 24 déc. 2015 à 09:37:36, Félix Cloutier via swift-evolution 
>  a écrit :
> 
> I like that it's consistent with the if syntax (even though I don't really 
> like the if syntax) and that there's no dangling parts after the else.
> 
> Félix
> 
>> Le 24 déc. 2015 à 06:29:17, Thorsten Seitz via swift-evolution 
>>  a écrit :
>> 
>> What do you think of
>> 
>> guard let r = returnsResult(), case let .Succeed(m) = r else {
>>   return r 
>> }
>> 
>> Which binds r only within the scope of the guard as desired.
>> 
>> Written in multiple lines
>> 
>> guard 
>>   let r = returnsResult(), 
>>   case let .Succeed(m) = r 
>> else {
>>   return r 
>> }
>> 
>> -Thorsten 
>> 
>>> Am 24.12.2015 um 01:02 schrieb Andrew Duncan via swift-evolution 
>>> :
>>> 
>>> Yes, which would revert to Brent’s suggestion. But you have generalized it 
>>> in a very compatible way.
>>> 
>>> As I read somewhere, improving programming languages comes from removing 
>>> limitations rather than adding features. I intend for this Pitch to be the 
>>> former, although it does kind of look like the latter.
>>> 
 On 23 Dec, 2015, at 15:58, Joe Groff  wrote:
 
 
> On Dec 23, 2015, at 3:56 PM, Andrew Duncan  wrote:
> 
> More progress! This sounds good, but it looks like what you intend is for 
> r to be the error message in the Result enum type.
> 
> enum Result {
> case .Fail(String)// Error message
> case .Succeed(MyType) // Something to work with
> }
> 
> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>  return r // Looks like r is bound to the error String. 
>   // But maybe you meant r = the entire returnsResult() result.
> }
 
 I see. If it's an arbitrary pattern, you can match 'case let r' to bind 
 the entire value instead of picking out the payload of the other case. 
 That would still be exhaustive.
 
 -Joe
 
> 
> The sort of message-passing error-handling I have in mind is where each 
> method in the call chain returns a full Result enum and each stage checks 
> it for Succeed/Fail, and immediately bails on Fail, returning 
> (propagating) the Result. To be sure, this is sort of what exceptions do 
> under the hood anyway.
> 
> My use-case is a recursive descent parser that I want to bail when a 
> syntax error is found. This could happen way deep in the stack of calls. 
> If I consistently return a .Fail(ErrorCode) or .Succeed(ASTNode) from 
> each method, I just pass on the Result in case of .Fail, or use it in 
> case of .Succeed.
> 
> 
>> On 23 Dec, 2015, at 15:35, Joe Groff  wrote:
>> 
>> 
>>> On Dec 23, 2015, at 10:16 AM, Andrew Duncan via swift-evolution 
>>>  wrote:
>> 
>> A slight generalization would be to allow for an arbitrary pattern in 
>> the `else` clause:
>> 
>> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>>  return r
>> }
>> 
>> with the requirement that the "guard" and "else" patterns form an 
>> exhaustive match when taken together. That feels nicer than special-case 
>> knowledge of two-case enums, though I admit it punishes what's likely to 
>> be a common case.
>> 
>> -Joe
>>> 
>>> ___
>>> swift-evolution mailing list
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>>> https://lists.swift.org/mailman/listinfo/swift-evolution
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>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 
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Re: [swift-evolution] [Pitch] Guarding on enum values

[Félix Cloutier via swift-evolution]

I feel exactly like Brent.

Félix

> Le 23 déc. 2015 à 04:15:24, Brent Royal-Gordon via swift-evolution 
>  a écrit :
> 
>>   guard case let .Succeed(m) = returnsResult() else {
>>return it
>>   }
>>   // Can safely use m, otherwise Result is passed back the call stack.
> 
> I didn't understand what you wanted to begin with, so to summarize: you want 
> to be able to bind the return value of `returnsResult()` to a constant on the 
> `else` branch if the pattern doesn't match.
> 
> I definitely see the use case here, but I can't say I like the implicit use 
> of `it`. If we did something like this, I would prefer it be done by 
> decorating the `else`:
> 
>   guard case let .Succeed(m) = returnsResult() else let r {
>   return r
>   }
> 
> However, I'm honestly not sure that's much less burdensome than this:
> 
>   let r = returnsResult()
>   guard case let .Succeed(m) = r else {
>   return r
>   }
> 
> It *is* a line less, and a constant less, but it also means adding a new and 
> slightly funky syntax to the language. I'm just not sure it's worth it.
> 
> -- 
> Brent Royal-Gordon
> Architechies
> 
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Re: [swift-evolution] [Pitch] Guarding on enum values

[Andrew Duncan via swift-evolution]

In fact, I feel the same way too. I have definite views about indefinite 
pronouns. When I am teaching, I studiously avoid “it”, “this”, and “that”: at 
any given instant half the students have wandering minds, and if they miss the 
referent, they get lost. My old HyperTalk habits must be resurfacing with “it”. 
:)

I still think the use case is valuable as a (natural IMHO) generalization of 
guard, and feel the annoyance of having the bound variable show up three times 
and outlast the guard, when I don’t want to use or even see it. Brent’s 
suggestion removes the second objection and alleviates the first; I’ll see 
that, but ask if we can raise it. The pitch is:

guard case let .Succeed(m) = returnsResult() else let r {
return r
}

Improvement! The question is: can we reduce this by one or two ‘r’s?

> On 23 Dec, 2015, at 6:59, Félix Cloutier  wrote:
> 
> I feel exactly like Brent.
> 
> Félix
> 
>> Le 23 déc. 2015 à 04:15:24, Brent Royal-Gordon via swift-evolution 
>>  a écrit :
>> 
>>>  guard case let .Succeed(m) = returnsResult() else {
>>>   return it
>>>  }
>>>  // Can safely use m, otherwise Result is passed back the call stack.
>> 
>> I didn't understand what you wanted to begin with, so to summarize: you want 
>> to be able to bind the return value of `returnsResult()` to a constant on 
>> the `else` branch if the pattern doesn't match.
>> 
>> I definitely see the use case here, but I can't say I like the implicit use 
>> of `it`. If we did something like this, I would prefer it be done by 
>> decorating the `else`:
>> 
>>  guard case let .Succeed(m) = returnsResult() else let r {
>>  return r
>>  }
>> 
>> However, I'm honestly not sure that's much less burdensome than this:
>> 
>>  let r = returnsResult()
>>  guard case let .Succeed(m) = r else {
>>  return r
>>  }
>> 
>> It *is* a line less, and a constant less, but it also means adding a new and 
>> slightly funky syntax to the language. I'm just not sure it's worth it.
>> 
>> -- 
>> Brent Royal-Gordon
>> Architechies
>> 
>> ___
>> swift-evolution mailing list
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>> https://lists.swift.org/mailman/listinfo/swift-evolution
> 

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Re: [swift-evolution] [Pitch] Guarding on enum values

[Andrew Duncan via swift-evolution]

Yes, which would revert to Brent’s suggestion. But you have generalized it in a 
very compatible way.

As I read somewhere, improving programming languages comes from removing 
limitations rather than adding features. I intend for this Pitch to be the 
former, although it does kind of look like the latter.

> On 23 Dec, 2015, at 15:58, Joe Groff  wrote:
> 
> 
>> On Dec 23, 2015, at 3:56 PM, Andrew Duncan  wrote:
>> 
>> More progress! This sounds good, but it looks like what you intend is for r 
>> to be the error message in the Result enum type.
>> 
>> enum Result {
>> case .Fail(String)// Error message
>> case .Succeed(MyType) // Something to work with
>> }
>> 
>> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>> return r // Looks like r is bound to the error String. 
>>  // But maybe you meant r = the entire returnsResult() result.
>> }
> 
> I see. If it's an arbitrary pattern, you can match 'case let r' to bind the 
> entire value instead of picking out the payload of the other case. That would 
> still be exhaustive.
> 
> -Joe
> 
>> 
>> The sort of message-passing error-handling I have in mind is where each 
>> method in the call chain returns a full Result enum and each stage checks it 
>> for Succeed/Fail, and immediately bails on Fail, returning (propagating) the 
>> Result. To be sure, this is sort of what exceptions do under the hood anyway.
>> 
>> My use-case is a recursive descent parser that I want to bail when a syntax 
>> error is found. This could happen way deep in the stack of calls. If I 
>> consistently return a .Fail(ErrorCode) or .Succeed(ASTNode) from each 
>> method, I just pass on the Result in case of .Fail, or use it in case of 
>> .Succeed.
>> 
>> 
>>> On 23 Dec, 2015, at 15:35, Joe Groff  wrote:
>>> 
>>> 
 On Dec 23, 2015, at 10:16 AM, Andrew Duncan via swift-evolution 
  wrote:
 
>>> 
>>> A slight generalization would be to allow for an arbitrary pattern in the 
>>> `else` clause:
>>> 
>>> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>>> return r
>>> }
>>> 
>>> with the requirement that the "guard" and "else" patterns form an 
>>> exhaustive match when taken together. That feels nicer than special-case 
>>> knowledge of two-case enums, though I admit it punishes what's likely to be 
>>> a common case.
>>> 
>>> -Joe
>> 
> 

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Re: [swift-evolution] [Pitch] Guarding on enum values

[Andrew Duncan via swift-evolution]

More progress! This sounds good, but it looks like what you intend is for r to 
be the error message in the Result enum type.

enum Result {
case .Fail(String)// Error message
case .Succeed(MyType) // Something to work with
}

guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
  return r // Looks like r is bound to the error String. 
   // But maybe you meant r = the entire returnsResult() result.
}

The sort of message-passing error-handling I have in mind is where each method 
in the call chain returns a full Result enum and each stage checks it for 
Succeed/Fail, and immediately bails on Fail, returning (propagating) the 
Result. To be sure, this is sort of what exceptions do under the hood anyway.

My use-case is a recursive descent parser that I want to bail when a syntax 
error is found. This could happen way deep in the stack of calls. If I 
consistently return a .Fail(ErrorCode) or .Succeed(ASTNode) from each method, I 
just pass on the Result in case of .Fail, or use it in case of .Succeed.
 

> On 23 Dec, 2015, at 15:35, Joe Groff  wrote:
> 
> 
>> On Dec 23, 2015, at 10:16 AM, Andrew Duncan via swift-evolution 
>>  wrote:
>> 
> 
> A slight generalization would be to allow for an arbitrary pattern in the 
> `else` clause:
> 
> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>   return r
> }
> 
> with the requirement that the "guard" and "else" patterns form an exhaustive 
> match when taken together. That feels nicer than special-case knowledge of 
> two-case enums, though I admit it punishes what's likely to be a common case.
> 
> -Joe

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Re: [swift-evolution] [Pitch] Guarding on enum values

[Joe Groff via swift-evolution]

> On Dec 23, 2015, at 3:56 PM, Andrew Duncan  wrote:
> 
> More progress! This sounds good, but it looks like what you intend is for r 
> to be the error message in the Result enum type.
> 
> enum Result {
> case .Fail(String)// Error message
> case .Succeed(MyType) // Something to work with
> }
> 
> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>  return r // Looks like r is bound to the error String. 
>   // But maybe you meant r = the entire returnsResult() result.
> }

I see. If it's an arbitrary pattern, you can match 'case let r' to bind the 
entire value instead of picking out the payload of the other case. That would 
still be exhaustive.

-Joe

> 
> The sort of message-passing error-handling I have in mind is where each 
> method in the call chain returns a full Result enum and each stage checks it 
> for Succeed/Fail, and immediately bails on Fail, returning (propagating) the 
> Result. To be sure, this is sort of what exceptions do under the hood anyway.
> 
> My use-case is a recursive descent parser that I want to bail when a syntax 
> error is found. This could happen way deep in the stack of calls. If I 
> consistently return a .Fail(ErrorCode) or .Succeed(ASTNode) from each method, 
> I just pass on the Result in case of .Fail, or use it in case of .Succeed.
> 
> 
>> On 23 Dec, 2015, at 15:35, Joe Groff  wrote:
>> 
>> 
>>> On Dec 23, 2015, at 10:16 AM, Andrew Duncan via swift-evolution 
>>>  wrote:
>>> 
>> 
>> A slight generalization would be to allow for an arbitrary pattern in the 
>> `else` clause:
>> 
>> guard case let .Succeed(m) = returnsResult() else case let .Failure(r) {
>>  return r
>> }
>> 
>> with the requirement that the "guard" and "else" patterns form an exhaustive 
>> match when taken together. That feels nicer than special-case knowledge of 
>> two-case enums, though I admit it punishes what's likely to be a common case.
>> 
>> -Joe
> 

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Re: [swift-evolution] [Pitch] Guarding on enum values

[Brent Royal-Gordon via swift-evolution]

> What about an enumeration with three cases? 
> 
> For example:
> 
> enum Result {
> case Success
> case Failure
> case Cancelled
> }

What about it? The case permitted by the `guard` continues through the 
surrounding scope; the other cases are handled by the `else` block.

-- 
Brent Royal-Gordon
Architechies

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Re: [swift-evolution] [Pitch] Guarding on enum values

[Step C via swift-evolution]

> On Dec 22, 2015, at 11:58 PM, Andrew Duncan via swift-evolution 
>  wrote:
> 
> Motivation
> 
> The guard statement rescues us from the pyramid of doom, and lets our code 
> hug the left margin more... if the failure case is false or nil. I'd like to 
> guard against specific values in an enum, and get the same flattening of code 
> flow. This generalizes Swift’s convenient handling of Optionals. (I have a 
> hazy perception that this was mooted for 1.x, but can’t remember where I read 
> it.)
> 
> The goal is to make error-handling by result-returning smoother. (I need say 
> no more about side-effect NSError** parameters.) Consider everyone’s favorite 
> enum example: 
> 
>enum Result { 
>case .Fail(String)  // Error message
>case .Succeed(MyType)   // Something we use.
>}
> 
> The Pitch (to avoid TL;DR)
> 
> I'd like to use something like this:
> 
>guard case let .Succeed(m) = returnsResult() else {
> return it
>}
>// Can safely use m, otherwise Result is passed back the call stack.

What about an enumeration with three cases? 

For example:

enum Result {
case Success
case Failure
case Cancelled
}


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Re: [swift-evolution] [Pitch] Guarding on enum values

[Brent Royal-Gordon via swift-evolution]

>guard case let .Succeed(m) = returnsResult() else {
> return it
>}
>// Can safely use m, otherwise Result is passed back the call stack.

I didn't understand what you wanted to begin with, so to summarize: you want to 
be able to bind the return value of `returnsResult()` to a constant on the 
`else` branch if the pattern doesn't match.

I definitely see the use case here, but I can't say I like the implicit use of 
`it`. If we did something like this, I would prefer it be done by decorating 
the `else`:

guard case let .Succeed(m) = returnsResult() else let r {
return r
}

However, I'm honestly not sure that's much less burdensome than this:

let r = returnsResult()
guard case let .Succeed(m) = r else {
return r
}

It *is* a line less, and a constant less, but it also means adding a new and 
slightly funky syntax to the language. I'm just not sure it's worth it.

-- 
Brent Royal-Gordon
Architechies

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