Rule 317

2007-10-23 Thread David Teller 
Hello list,

 I'm still fighting the syntax of JS2. Attempting to feed it into a
parser generator (menhir, for the moment), has already allowed me to
find a few typoes in the spec and a few useless variables in the
reference implementation, which is all I have to show for the moment.
That and the fact that all XML* productions seem absent from the RI.

At the moment, though, I'm being puzzled by rule 317:

ExpressionStatement
|  ListExpression (allowColon, allowIn) 
   [if lookahead not in { function, let, { }]

Besides the fact that this rule is annoying to implement, does it
actually mean what it intends ? In addition to blocks, it also prevents
an assignment to an object pattern from starting the ListExpression. Is
that desired ?

Thanks,
 David

P.S.:
 I forgot where I found that version of the grammar, it's dated
14/10/2007, so I assume it's the latest. Where are they to be found, in
general ?

-- 
David Teller --
Security of Distributed Systems ---
Project JStify: Static Analysis for JavaScript 2  -
-- http://www.univ-orleans.fr/lifo/Members/David.Teller
- Laboratoire d'Informatique Fondamentale d'Orleans

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Re: Rule 317

2007-10-23 Thread David Teller 
On Tue, 2007-10-23 at 14:58 +0200, liorean wrote:
 It's there to prevent the grammar from being ambiguous. function,
 let and { have different meaning in statement context from
 expression context. If the ExpressionStatement construct allowed them,
 then they would be ambigous in statement context, they could have
 either the statement or the expression semantics. So, in order to
 prevent this ambiguity, they are not allowed in ExpressionStatement.

So I guess this could just be handled by making this rule have a lowest
priority ?


Cheers,
 David

-- 
David Teller --
Security of Distributed Systems ---
Project JStify: Static Analysis for JavaScript 2  -
-- http://www.univ-orleans.fr/lifo/Members/David.Teller
- Laboratoire d'Informatique Fondamentale d'Orleans

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Re: Rule 317

2007-10-23 Thread liorean 
 On Tue, 2007-10-23 at 14:58 +0200, liorean wrote:
  It's there to prevent the grammar from being ambiguous. function,
  let and { have different meaning in statement context from
  expression context. If the ExpressionStatement construct allowed them,
  then they would be ambigous in statement context, they could have
  either the statement or the expression semantics. So, in order to
  prevent this ambiguity, they are not allowed in ExpressionStatement.

On 23/10/2007, David Teller [EMAIL PROTECTED] wrote:
 So I guess this could just be handled by making this rule have a lowest
 priority ?

Not really. In statement context, a function without a name should be
a syntax error, it shouldn't be handled as function expression because
that'd be pointless. If the function object is only accessible through
the return value of the function expression but it's in statement
context - i.e. return values are thrown away - then compiling the
function at all is totally pointless, you're just adding a
non-reachable object for the garbage collector to deal with. In a
statement context, { is a block opener and not the beginning of an
object literal. In a block statement Identifier : is a label
statement and not a property assignment. *string* : is a syntax
error because : is not a valid operator there. (Not sure how type
annotations play into this, I might be wrong here...)

So you see, they can't just be lowest priority. They must fail with a
syntax error. For ES3 compatibility's sake, if nothing else. Also,
it's better to not let nonsensical constructs be allowed.
-- 
David liorean Andersson
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