Commit af3bd6e2 authored by POTTIER Francois's avatar POTTIER Francois
Browse files

Remove the redundancy between StackSymbols and Invariant.

parent dd17fa7b
Pipeline #187980 passed with stages
in 1 minute and 14 seconds
......@@ -17,47 +17,8 @@
open Grammar
module C = Conflict (* artificial dependency; ensures that [Conflict] runs first *)
(* ------------------------------------------------------------------------ *)
(* Compute a lower bound on the height of the stack at every state. At the
same time, compute which symbols are held in this stack prefix. *)
(* In order to compute (a lower bound on) the height of the stack at a state
[s], we examine the LR(0) items that compose [s]. For each item, if the
bullet is at position [pos], then we can be assured that the height of the
stack is at least [pos]. Thus, we compute the maximum of [pos] over all
items (of which there is at least one). *)
(* The set of items that we use is not closed, but this does not matter; the
items that would be added by the closure would not add any information
regarding the height of the stack, since the bullet is at position 0 in
these items. *)
(* Instead of computing just the stack height, we compute, in the same manner,
which symbols are on the stack at a state [s]. This is an array of symbols
whose length is the height of the stack at [s]. By convention, the top of
the stack is the end of the array. *)
(* We first compute and tabulate this information at the level of the LR(0)
automaton. *)
(* This analysis is extremely fast: on an automaton with over 100,000 states,
it takes under 0.01 second. *)
let stack_symbols : Lr0.node -> Symbol.t array =
let dummy =
Array.make 0 (Symbol.T
Misc.tabulate Lr0.n (fun node ->
Item.Set.fold (fun item accu ->
let _prod, _nt, rhs, pos, _length = Item.def item in
if pos > Array.length accu then Array.sub rhs 0 pos else accu
) (Lr0.items node) dummy
(* Then, it is easy to extend it to the LR(1) automaton. *)
let stack_symbols (node : Lr1.node) : Symbol.t array =
stack_symbols (Lr0.core (Lr1.state node))
let stack_symbols =
let stack_height (node : Lr1.node) : int =
Array.length (stack_symbols node)
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