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Commit bdc39e5f authored by POTTIER Francois's avatar POTTIER Francois
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Removed [Coverage] entirely. Committing to [LRijkstra] instead.

parent d4ee9881
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(* The purpose of this algorithm is to find, for each pair of a state [s]
and a terminal symbol [z] such that looking at [z] in state [s] causes
an error, a minimal path (starting in some initial state) that actually
triggers this error. *)
(* This is potentially useful for grammar designers who wish to better
understand the properties of their grammar, or who wish to produce a
list of all possible syntax errors (or, at least, one syntax error in
each automaton state where an error may occur). *)
(* The problem seems rather tricky. One might think that it suffices to
compute shortest paths in the automaton, and to use [Analysis.minimal] to
replace each non-terminal symbol in a path with a minimal word that this
symbol generates. One can indeed do so, but this yields only a lower bound
on the actual shortest path to the error at [s, z]. Indeed, two
difficulties arise:
- Some states have a default reduction. Thus, they will not trigger
an error, even though they should. The error is triggered in some
other state, after reduction takes place.
- If the grammar has conflicts, conflict resolution removes some
(shift or reduce) actions, hence may suppress the shortest path. *)
(* We explicitly choose to ignore the [error] token. If the grammar mentions
[error] and if some state is reachable only via an [error] transition, too
bad: we report this state as unreachable. It would be too complicated to
have to create a first error in order to be able to take certain
transitions or drop certain parts of the input. *)
open Grammar
module W = Terminal.Word(struct end) (* TEMPORARY wrap side effect in functor *)
......@@ -924,15 +954,8 @@ let () =
count the unreachable states and see if they are numerous in practice
optionally report several ways of reaching an error in state s
(with different lookahead tokens) (report all of them?)
warn if --coverage is set AND the grammar uses [error]
implement a naive semi-algorithm that enumerates all input sentences,
and evaluate how well (or how badly) it scales
(* One could approach the problem just by exploring the (infinite) graph whose
vertices are configurations of the LR automaton (i.e., stacks, or perhaps
pairs of a stack and a lookahead symbol) and transitions are determined by
feeding one symbol to the automaton. A small-step version of the reference
interpreter would allow us to set this up easily. One could then run a
breadth-first exploration of this graph and stop when desired, e.g., as
soon as all automaton states have been reached. However, this process does
not necessarily terminate, and could be very costly -- e.g. enumerating all
sentences of length 10 when the alphabet has size 100 costs 10^20. Also,
this approach cannot prove that a state is unreachable. *)
......@@ -4,5 +4,4 @@
module B = Back (* artificial dependency *)
(*module C = Coverage (*TEMPORARY*)*)
module L = LRijkstra (* TEMPORARY *)
......@@ -230,8 +230,8 @@ let interpret log nt lexer lexbuf =
(* ------------------------------------------------------------------------ *)
(* Another entry point, used internally by [Coverage] to check that the
sentences that [Coverage] produces do lead to an error in the expected
(* Another entry point, used internally by [LRijkstra] to check that the
sentences that [LRijkstra] produces do lead to an error in the expected
state. *)
open MenhirLib.General (* streams *)
......@@ -20,7 +20,7 @@ val interpret:
cst option
(* This variant of the reference interpreter is used internally by us. We use
it to debug [Coverage]. It checks that a sentence leads to a syntax error
it to debug [LRijkstra]. It checks that a sentence leads to a syntax error
in the expected state. *)
type check_error_path_outcome =
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