JimPoints out also that we should not be guarding our scope stacks.
Let's begin with the guards we added for referencing rule properties.
In version 3.0.1, if the else clause is not executed, s is null and
you get a null pointer at $s.st.
('else' s=stat)? ... {$s.st}
For 3.1, we have guarded all of those property references with s!=null?
s.st:null. That is good.
Now Imagine how we guard stack stuff. consider the following rule:
block
scope { int x; }
: '{' stat+ '}'
;
Ref $block::x currently checks that the stack is not empty before
calling peek() to avoid a stack underflow exception. Jim argues that
we should take that guard back out because it is a programming error
to refer to $block::x when the stack is not properly set up. I think
I'm agreeing with him. Is like accessing the local variable in an
enclosing function but when there is no invoking function.
We would need to change these templates:
scopeAttributeRef(scope,attr,index,negIndex) ::= <<
<if(negIndex)>
((<scope>_stack.size()-<negIndex>-1)>=0?
((<scope>_scope)<scope>_stack.elementAt(<scope>_stack.size()-
<negIndex>-1)).<attr.name>:<initValue(attr.type)>)
<else>
<if(index)>
((<index>\<<scope>_stack.size())?
((<
scope
>
_scope
)<scope>_stack.elementAt(<index>)).<attr.name>:<initValue(attr.type)>)
<else>
((<scope>_stack.size()>0)?
((<
scope>_scope)<scope>_stack.peek()).<attr.name>:<initValue(attr.type)>)
<endif>
<endif>
>>
scopeSetAttributeRef(scope,attr,expr,index,negIndex) ::= <<
if ( <scope>_stack.size()>0 ) {
<if(negIndex)>
((<scope>_scope)<scope>_stack.elementAt(<scope>_stack.size()-
<negIndex>-1)).<attr.name> =<expr>;
<else>
<if(index)>
((<scope>_scope)<scope>_stack.elementAt(<index>)).<attr.name> =<expr>;
<else>
((<scope>_scope)<scope>_stack.peek()).<attr.name> =<expr>;
<endif>
<endif>
}
>>
to avoid (<scope>_stack.size()>0) tests.
Is it okay for me to remove the stack guards for dynamic scoping
stuff? quick change to these two templates.
Ter
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