lang lr0 - Guile Reference Manual

— Scheme Procedure: grammar-item-table g

Return the item table for grammar g, making it if necessary.
Every grammar is given an item table: a vector of all items associated with the grammar. An item's position in this table is called the item's "index".
The extent of the table is tied to the extent of g, and the extent of items to the table. For a given production, and position, make-item (see below) will always return eq? items from the item-table of the grammar.

— Scheme Procedure: item-set-start-kernel g

Return the kernel of the starting superstate for grammar g. This is an item-set of sorts.
Only the initial items of start-symbol productions are included in this set. Compose with item-set-closure to also obtain all items reachable by epsilon transitions.

— Scheme Procedure: item-set-successor-kernel g is symbol

For grammar g, with item-set is, shift symbol symbol and return the resulting (possibly empty) item-set.
Only the items which are direct successors of items in is are present in the successor kernel. To also include all items reachable by epsilon transitions, use item-set-closure.

— Scheme Procedure: item-set-reductions g is

For grammar g, return the (possibly empty) set of all productions that can be reduced from item-set is, disregarding the context and look-ahead.

— Scheme Procedure: item-set-closure g is

For grammar g, return the epsilon transition closure of item set is.
In the LR(0) NFA, if we are at the state:
                  A -> w * B v
Then we are also an epsilon transition (not to be confused with an empty reduction) away from also being in the items:
                  B -> * u
                  B -> * r
                  B -> * s
                  ...
So if a superstate contains A->w*Bv, then it should also contain the inital states of B. This rule applies transitively.
If is was returned by item-set-start-kernel, then this procedure returns the DFA start state.
If is was returned by item-set-successor-kernel, and the IS argument to item-set-successor-kernel was a DFA state, then this procedure returns a DFA state.

There is also a drop-in replacement for (lang lr0) that provides some additional debugging facilities: (lang lr0-debug).

— Scheme Procedure: VALIDATE:production obj

Check production-specific invariants for obj. If there is a problem, signal error with message of the form:
          supposed production INVARIANT-ERROR
where invariant-error is one of:

not a list
has length not >= 2
car not a symbol
cadr not a list of symbols

— Scheme Procedure: VALIDATE:item obj

Check item-specific variants for obj. If there is a problem, signal error with message of the form:
          supposed item INVARIANT-ERROR
where invariant-error is one of:

not a list
cdr CDR not a subset of the expansion EXPANSION

— Scheme Procedure: VALIDATE:item-set obj

Check item-set-specific variants for obj. If there is a problem, signal error with message of the form:
          supposed item-set INVARIANT-ERROR
where invariant-error is one of:

not a list
Additionally, check each member of the item-set with VALIDATE:item.

— Scheme Procedure: grammar-with-nicknames grammar

Decorate grammar productions with nicknames and return it. For each production, call VALIDATE:production on it and then decorate with a string of the form "PRODUCTION-SYMBOL[ADDRESS]".

41.3 LR(0) parser