Hi Cliff, thanks for the input. I think it might be hard to record complete
"state of the lexer" for each input position efficiently. Users could, for
example, update a large global data structure as they lexed.
Hmm...yeah, i was trying this idea earlier but we sort of need to formalize
arguments to parser rules to handle predicates that get generated outside of
the defining function (when I need to gen cyclic DFA). THis happens for Java
as it has no goto. might as well do locals too.
T
On Apr 18, 2010, at 4:04 PM, Cliff Hudson wrote:
> With respect to local variables and actions in ambiguous sets of rule, it
> seems to me that the entire rule alternative is the scope for all actions
> which appear in it, so having an action which declares a variable and then
> another action later in the alternative which executes some code is really
> all one method. What would need to be dealt with is that the language target
> generator would need to be able to take the state pulled from the DFA and
> insert that information into the alternative's action sequence so that each
> action had access to the logical state at the time it executes.
>
> For instance, in the rule:
>
> FOO: { int n=4; } 'a'* { n += $text.Length; } 'bcd' { System.WriteLine("{0}:
> {1}", n, $text); } ;
>
> the alternative's action function would look like:
>
> foo_alt1(State[] states)
> {
> int n=4;
> n += states[0].Text.Length;
> System.WriteLine("{0}: {1}", n, states[1].Text);
> }
>
> The State[] is an output from the DFA. Ambiguity then doesn't have any
> effect on your ability to execute actions, but language targets would need to
> be rewritten.
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