2 Yacc Qs

1. Is there a Yacc FAQ or listserv?


--------------------
2. Specific Yacc Q:


I am building an expression grammar and having problems with associativity
and shift/reduce conflicts. The language I am emulating permits a statement
like this:


    set y to items 1 thru 2 of x as string


which should be read as: "set y to (items 1 thru 2 of x) as string"
and not as: "set y to items 1 thru 2 of (x as string)"




My grammar always picks the 2nd path. The relevant rules look like this:


statement:
      SET IDENT TO expression


expression:
      object_specifier
  | IDENT
  | expression AS class


object_specifier:
      object_container
  | object_container of expression
  | object_container of object_specifier


object_container:
      class
  | class expression THRU expression




The order of rules triggered (caps denote tokens passed in from Lex):


    set y to item 1 thru 2 of x as string


class: CLASS // "item"
expression: INTEGER
object_container: class expression THRU expression
expression: INTEGER
expression: IDENT // next we'd want "obj_spec: obj_cont of expr" but...
class: CLASS
expression: expression AS class
object_specifier: object_container of expression
expression: object_specifier
statement: SET IDENT TO expression




I have read everything the Levine book has to say about associativity and
precedence, and I have tried all the tricks I know of reordering, defining
explicit case rules, and using %prec (although I'm not sure I use %prec
correctly).


Can anyone offer any hints or help? Thanks very much.


-----------------------------------------------------------------
Barton Jaques Zero Divide Software zero@istar.ca
[These precedence questions drive me crazy, and I have to admit that yacc
doesn't offer much help. -John]
--

Return to the comp.compilers page.
Search the comp.compilers archives again.