[swift-dev] Implementing New Syntax in Swift

Seth Friedman sethfri at gmail.com
Sun Jan 17 18:13:38 CST 2016

Created SR-569 <https://bugs.swift.org/browse/SR-569> to track this



On Sun, Jan 10, 2016 at 4:18 PM, Seth Friedman <sethfri at gmail.com> wrote:

> Changing the subject of this thread since it's now an entirely different
> question than what I originally asked. Hopefully this will result in better
> visibility in getting an answer as well.
> Thanks,
> Seth
> On Sun, Jan 10, 2016 at 4:16 PM Seth Friedman <sethfri at gmail.com> wrote:
>> Thanks Jordan!
>> Here's a specific flow I'm interested in understanding. Note that this is
>> just a wild example that would help me better understand parts of the
>> compiler I'm interested in rather than any sort of proposal for the
>> language.
>> Let's say I have a type called SuperInt that has some cool integer
>> operations that would be applicable and useful to everyone writing Swift.
>> It's a given that this makes sense to be in the Swift language, and people
>> are going to be using it so often that it makes sense to create a new
>> literal syntax for this type. I'd like users to be able to instantiate a
>> SuperInt with the following:
>> let superIntExample = %^100^%
>> Crazy syntax for a crazy example, but I wanted to make sure it's not
>> something that's already in Swift. In this example, my SuperInt would be
>> instantiated with a value of 100.
>> I'd like to know the parts of the Swift compiler I would need to
>> understand and change to implement this new type with its new syntax.
>> I really this question requires a lengthy answer, but I think it would
>> make a great start to a Swift internals manual (which I agree with you
>> would be a fantastic idea).
>> Anyone's help would be much appreciated!
>> Thanks,
>> Seth
>> On Fri, Dec 18, 2015 at 5:25 PM Jordan Rose <jordan_rose at apple.com>
>> wrote:
>>> Hi, Seth. Sorry for not getting back to you sooner! I don't think we
>>> have anything exactly like this, but there's *sort* of a sequence
>>> diagram in Chris and Joe's talk at the LLVM conference, "Swift's
>>> High-Level IR <https://youtu.be/Ntj8ab-5cvE>". I'd say it looks
>>> something like this:
>>> 1. Parsing
>>> 2. Semantic analysis, including type-checking
>>> 3. SIL generation
>>> 4. Mandatory SIL passes
>>> 5. SIL optimization
>>> 6. LLVM IR generation
>>> 7. LLVM optimization
>>> 8. LLVM output (usually including machine code generation and writing to
>>> a .o file)
>>> …with the last two handled pretty much completely by LLVM
>>> <http://llvm.org> itself, and not customized by Swift.
>>> We probably ought to have something like Clang's "Internals
>>> <http://clang.llvm.org/docs/InternalsManual.html>" manual (hopefully
>>> better), which lays out the major concepts in each library. As it is we
>>> have various concepts that are documented very well, either in docs/ or in
>>> header comments, and others which are just arcane knowledge in the heads of
>>> the implementers. This is not a good thing.
>>> The "Contributing <https://swift.org/contributing/>" page on the
>>> website lists a handful of ways to get involved; another one we're still
>>> bringing up is issues with the "StarterBug" label in JIRA. These are
>>> intended to be bugs that a newcomer could use as a goal-oriented way to
>>> learn about one part of the project.
>>> Of course, we're happy to answer any specific questions you might have
>>> (and this list is probably the right place for them). It's the general ones
>>> that are hard. :-)
>>> Jordan
>>> On Dec 16, 2015, at 2:36, Seth Friedman <sethfri at gmail.com> wrote:
>>> Thanks Jordan!
>>> Another question if anyone has some time: I'm really interested in
>>> contributing to the project, but given that I don't have a ton of
>>> experience with compilers, I'm having a really hard time following the flow
>>> of the program. I understand that the high level flow is lexing, parsing,
>>> sema, and building the AST. However, tracing through the actual functions
>>> in the compiler prove much more difficult due to the amount of
>>> indirection/metaprogramming.
>>> Are there any sort of sequence diagrams that I haven't found yet? If
>>> anyone could let me know of any good resources you know of, that would be
>>> great. I'm sure this would also be of use to people in my boat that want to
>>> help but don't know how to start.
>>> Thanks,
>>> Seth
>>> On Tue, Dec 8, 2015 at 9:04 PM Jordan Rose <jordan_rose at apple.com>
>>> wrote:
>>>> Hi, Seth. I think you're getting Clang / swift-clang mixed up with
>>>> swiftc / swift. Clang is not the Swift compiler; the Swift compiler lives
>>>> in the "swift" repo. Swift depends on Clang for its interoperation with C
>>>> and Objective-C.
>>>> A *lot* of the compiler encodes information about Optional, but most
>>>> of it stems from ASTContext.h and ASTContext.cpp, which has dedicated
>>>> entrypoints for getting Optional, Optional.None, and Optional.Some.
>>>> Hope this helps,
>>>> Jordan
>>>> On Dec 8, 2015, at 17:59 , Seth Friedman via swift-dev <
>>>> swift-dev at swift.org> wrote:
>>>> Hi all,
>>>> In Optional.swift in the stdlib, there's a comment that says "The
>>>> compiler has special knowledge of Optional<Wrapped>, including the fact
>>>> that it is an enum with cases named 'None' and 'Some'."
>>>> What I'm trying to understand is: If I wanted to implement the optional
>>>> type from scratch, what would be the process I would go through? I've
>>>> scoured the swift-clang project and can't seem to find any reference to
>>>> optionals or even Swift explicitly. I discovered nullability attributes and
>>>> am hypothesizing that an expression of something like "Type?" is somehow
>>>> mapped to an attribute, but I'm really just stumbling around in the dark.
>>>> In terms of what I've tried, I've gone through a lot of the source in
>>>> the swift-clang lib/Basic and lib/AST directories, and I've read through
>>>> the "Clang CFE Internals Manual" on the Clang website.
>>>> Help is much appreciated!
>>>> Thanks in advance,
>>>> Seth
>>>> _______________________________________________
>>>> swift-dev mailing list
>>>> swift-dev at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-dev

Seth Friedman
*Software Development Engineer II*
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