Hi Greg,
Thanks very much for the clear answer. This helps me a lot!
Best regards,
Toni
> On 23 Mar 2016, at 17:53, Greg Titus <g...@omnigroup.com> wrote:
>
> Hi Toni,
>
> What you are seeing is a side-effect of / workaround for the use of top-level
> executable statements.
>
> In general, at the top level of a source file you expect declarations (of
> types, of functions, etc) and then statements will be inside those
> declarations (the implementations of free functions or members, etc). Various
> portions of the type checker and AST checker depend on these assumptions —
> that scanning through the top-level parts of a source file will be all
> declarations, and conversely, that every statement will be inside braces
> (e.g. “{}”) to control scopes and so on.
>
> When compiling in library-mode, this setup is always true. But when compiling
> for playgrounds/tools/etc you can have executable statements at the top
> level. In order to keep the expected invariants of declarations on top and
> statements inside, top_level_code_decl is a declaration that contains a
> brace_stmt that contains the parsed top-level executable statements.
>
> And then finally, because you are declaring a variable “x” that ought to be
> visible further down in the file, the var_decl, which would normally be in
> the scope inside the braces in a ‘normal’ declaration is emitted at the top
> level as well.
>
> In short, the AST for this kind of thing is a bit weird looking in order to
> preserve expected structure invariants of the tree.
>
> Hope this helps!
> - Greg
>
>> On Mar 23, 2016, at 5:58 AM, Toni Suter via swift-dev <swift-dev@swift.org
>> <mailto:swift-dev@swift.org>> wrote:
>>
>> Hi,
>>
>> I am trying to understand the Swift AST by looking at output produced from
>> swiftc -dump-ast <file>.
>> Most of it makes sense to me, but there are some things that I don’t
>> understand. For example, consider
>> the following code:
>>
>> var x = 42
>>
>> This produces the following output:
>>
>> (source_file
>> (top_level_code_decl
>> (brace_stmt
>> (pattern_binding_decl
>> (pattern_named type='Int' 'x')
>> (call_expr implicit type='Int' location=test.swift:1:9
>> range=[test.swift:1:9 - line:1:9] nothrow
>> (constructor_ref_call_expr implicit type='(_builtinIntegerLiteral:
>> Int2048) -> Int' location=test.swift:1:9 range=[test.swift:1:9 - line:1:9]
>> nothrow
>> (declref_expr implicit type='Int.Type ->
>> (_builtinIntegerLiteral: Int2048) -> Int' location=test.swift:1:9
>> range=[test.swift:1:9 - line:1:9]
>> decl=Swift.(file).Int.init(_builtinIntegerLiteral:) specialized=no)
>> (type_expr implicit type='Int.Type' location=test.swift:1:9
>> range=[test.swift:1:9 - line:1:9] typerepr='Int'))
>> (tuple_expr implicit type='(_builtinIntegerLiteral: Int2048)'
>> location=test.swift:1:9 range=[test.swift:1:9 - line:1:9]
>> names=_builtinIntegerLiteral
>> (integer_literal_expr type='Int2048' location=test.swift:1:9
>> range=[test.swift:1:9 - line:1:9] value=42))))
>> ))
>> (var_decl "x" type='Int' access=internal storage_kind=stored))
>>
>> Intuitively, I would have expected that the initializer is part of the
>> var_decl. Also, why is there a brace_stmt involved?
>> As far as I have seen, the term brace statement doesn’t appear anywhere in
>> the Swift Language Reference. Is it the
>> same as code-block
>> <https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Declarations.html#//apple_ref/swift/grammar/code-block>?
>>
>> Thanks in advance!
>>
>> Best regards,
>> Toni
>> _______________________________________________
>> swift-dev mailing list
>> swift-dev@swift.org <mailto:swift-dev@swift.org>
>> https://lists.swift.org/mailman/listinfo/swift-dev
>
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