[Qt-qml] documenting the Qml grammar

[aaron.kennedy at nokia.com]

Hi,


On 18/05/10 11:02 PM, "Kamm Christian.D (Nokia-D/Berlin)"
<christian.d.kamm at nokia.com> wrote:
> I think it'd be good to have an annotated grammar of the Qml language in the
> documentation. The current way of teaching by example is great for new users.
> It isn't very good as a quick reference, a reliable way to resolve corner
> cases or to figure out whether something is valid Qml.

Great!  I've started on this a number of times, but never really got
anywhere before being distracted.  Perhaps someone with more discipline will
have more luck.

> QmlProgram:
>     QmlImport* QmlObjectDefinition
> 
> QmlImport:
>     'import' QmlImportId QmlImportVersion ('as' QmlIdentifier)?
>     'import' StringLiteral QmlImportVersion? ('as' QmlIdentifier)?
> 
> QmlImportId:
>     IdentifierName ('.' IdentifierName)*
> 
> The implemented grammar just says "QmlImportId: MemberExpression" and has an
> extra check to verify it's either a string literal or a series of
> FieldMemberExpressions in the parsing code. I think this should be explicit in
> the documentation. It may also be worthwhile to change the grammar like this
> to allow using reserved words for qualified imports.

Agreed.

> QmlImportVersion:
>     DecimalIntegerLiteral '.' DecimalDigits
> 
> The implemented grammar uses NumericLiteral here. Being more explicit shows
> that 1.5e9 is not a valid import version more clearly.

Sure, if you're happy to type "import Qt 4.1500000000" in another 1499999993
releases of Qt :)  Ok, DecimalDigits makes more sense.

> QmlObjectMember:
>     QmlPropertyDeclaration
>     QmlPropertyBinding
>     QmlObjectDefinition
>     QmlSignalDeclaration
>     FunctionDeclaration
> 
> Omitted VarDeclaration.

Do you mean the "UiObjectMember: VariableStatement" clause?  I think that
should be removed.  Roberto?

> QmlPropertyDeclaration:
>     'property' QmlPropertyType QmlIdentifier (':' QmlPropertyRhs)?
>     'property' 'list' '<' QmlQualifiedId '>' (':' '[' QmlArrayMemberList?
> ']')?
>     'default' 'property' 'alias' QmlIdentifier ':' QmlPropertyRhs
> 
> This is different from the implemented grammar in several ways.
> 
> 1. It allows any right-hand side that's valid in a property binding as the
> initializer of a declaration. While separating the two may make sense to
> programmers, what's the harm in making
> 
>   property int foo : 3*width
> 
> be equivalent to the following:
> 
>   property int foo
>   foo: 3*width

It *should* be the same.  I thought this had been fixed, but I guess not :(

> 2. I changed the list type from list<QmlIdentifier> to list<QmlQualifiedId> to
> allow lists of types that have been imported into a namespace. This seems to
> be an oversight in the current implementation.

Yep

> 3. is there any use for 'default' properties that don't have 'alias' type? I
> couldn't think of any and altered the grammar accordingly.

Object and list properties can be default.  "default property Object blah"
for example.

> QmlPropertyType:
>     QmlIdentifier
> 
> I dropped ReservedWord and 'var'. The latter is deprecated and no Qml types
> seem to be reserved words.

Ok.

> I'll open tickets for these bugs/suggestions in a few days, depending on the
> feedback.

Please do.

Cheers,

Aaron