problem with declaration grammar?

[jerry quinn]

Sergey Gromov Wrote:

> Thu, 19 Feb 2009 01:30:36 -0500, jerry quinn wrote:
> 
> > Christopher Wright Wrote:
> > 
> >> jerry quinn wrote:
> >>> Hi there,
> >>> 
> >>> I'm not sure if I'm missing something, but I'm having trouble seeing that a simple declaration will parse correctly with the D grammar.
> >>> 
> >>> If we take a declaration statment like:
> >>> 
> >>> int x = 3;
> >>> 
> >>> we have (my best guess):
> >>> 
> >>> DeclarationStatement -> Declaration
> >>> Declaration -> Decl
> >>> Decl -> BasicType Declarators ;
> >>> BasicType -> int
> >>> Declarators -> DeclaratorInitializer
> >>> DeclaratorInitializer -> Declarator = Initializer
> >>> Declarator -> BasicType2 Identifier
> >>> BasicType2 -> ????
> >>> 
> >>> I'm thinking that BasicType2 is optional here, rather than required as the grammar shows.  Is that correct?
> >>> 
> >>> Thanks
> >>> Jerry
> >> 
> >> . Declaration -> Decl
> >> . Decl -> BasicType Declarators
> >> . BasicType -> "int"
> >> . Declarators -> DeclaratorInitializer
> >> . DeclaratorInitializer -> Declarator "=" Initializer
> >> We agree up to here.
> >> 
> >> . Declarator -> Identifier
> >> Here, you don't need BasicType2, and if you use it, you recurse, so 
> >> using the rule Declarator -> BasicType2 Declarator here is useless.
> > 
> > What you describe sounds like what I'd expect.
> > 
> > Maybe I'm missing something.  The grammar shown in http://www.digitalmars.com/d/2.0/declaration.html has the following rules:
> > 
> > BasicType2:
> >         *
> >         [ ]
> >         [ Expression ]
> >         [ Expression .. Expression ]
> >         [ Type ]
> >         delegate Parameters FunctionAttributesopt
> >         function Parameters FunctionAttributesopt
> > 
> > Declarator:
> >         BasicType2 Declarator DeclaratorSuffixesopt
> >         BasicType2 Identifier DeclaratorSuffixesopt
> > 
> > With this definition, I don't see how you can get Declarator->Identifier.
> > 
> > Jerry
> 
> The grammar works the other way around:
> 
> int x = 3 ;
> 
> int -> BasicType(int)
> // this is either Decl or Type, need more tokens, expect Declarators,
> // Declarator, or Declarator2
> -----
> x -> Identifier(x)
> // either DeclaratorInitializer (Declarators), Declarator,
> // IdentifierList (not expecting), StructMemberInitializer (not
> // expecting), or PrimaryExpression (not expecting)
> // therefore expecting '=' or DeclaratorSuffixes
> -----
> = -> = // token
> // Identifier(x) = -> definitely DeclaratorInitializer, expecting
> // Initializer, that is , either void, AssignExpression,
> // ArrayInitializer, or StructInitializer

This is incorrect.  We have

 BasicType(int) Identifier(x) '= '

You're suggesting the Identifier begins DeclaratorInitializer, but it must start with a Declarator.  We don't have one, because Declarator must start with BasicType2.  This is where I think the bug in the grammar is.  If BasicType2 were optional, then the parse would complete as you showed.

> Finita la comedia.

Unfortunately, not yet fini