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java: add support for lookahead correction

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Shamelessly stolen from Adrian Vogelsgesang's implementation in
lalr1.cc.

* data/skeletons/lalr1.java (yycdebugNnl, yyLacCheck, yyLacEstablish)
(yyLacDiscard, yylacStack, yylacEstablished): New.
(Context): Use it.
* examples/java/calc/Calc.y: Enable LAC.
This commit is contained in:
Akim Demaille
2020-11-01 19:21:27 +01:00
parent 787052f074
commit c223baee63
2 changed files with 220 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

233
data/skeletons/lalr1.java
View File

@@ -1,4 +1,4 @@
# Java skeleton for Bison -*- autoconf -*-
# Java skeleton for Bison -*- java -*-
# Copyright (C) 2007-2015, 2018-2020 Free Software Foundation, Inc.
@@ -80,6 +80,15 @@ m4_define([b4_define_state],
]b4_yystype[ yylval = null;
]])
# parse.lac
b4_percent_define_default([[parse.lac]], [[none]])
b4_percent_define_check_values([[[[parse.lac]], [[full]], [[none]]]])
b4_define_flag_if([lac])
m4_define([b4_lac_flag],
[m4_if(b4_percent_define_get([[parse.lac]]),
[none], [[0]], [[1]])])
## ------------- ##
## Parser File. ##
## ------------- ##
@@ -93,6 +102,7 @@ b4_output_begin([b4_parser_file_name])[
]b4_user_pre_prologue[
]b4_user_post_prologue[
import java.text.MessageFormat;
import java.util.Vector;
]b4_percent_code_get([[imports]])[
/**
* A Bison parser, automatically generated from <tt>]m4_bpatsubst(b4_file_name, [^"\(.*\)"$], [\1])[</tt>.
@@ -257,8 +267,10 @@ import java.text.MessageFormat;
*/
public ]b4_parser_class[(]b4_parse_param_decl([b4_lex_param_decl])[)]b4_maybe_throws([b4_init_throws])[
{
]b4_percent_code_get([[init]])[
this.yylexer = new YYLexer (]b4_lex_param_call[);
]b4_percent_code_get([[init]])[]b4_lac_if([[
this.yylacStack = new Vector<Integer>();
this.yylacEstablished = false;]])[
this.yylexer = new YYLexer(]b4_lex_param_call[);
]b4_parse_param_cons[
}
]])[
@@ -269,7 +281,9 @@ import java.text.MessageFormat;
*/
]b4_lexer_if([[protected]], [[public]]) b4_parser_class[(]b4_parse_param_decl([[Lexer yylexer]])[)]b4_maybe_throws([b4_init_throws])[
{
]b4_percent_code_get([[init]])[
]b4_percent_code_get([[init]])[]b4_lac_if([[
this.yylacStack = new Vector<Integer>();
this.yylacEstablished = false;]])[
this.yylexer = yylexer;
]b4_parse_param_cons[
}
@@ -338,6 +352,11 @@ import java.text.MessageFormat;
yylexer.yyerror(new ]b4_location_type[ (pos), msg);
}]])[
]b4_parse_trace_if([[
protected final void yycdebugNnl(String s) {
if (0 < yydebug)
yyDebugStream.print(s);
}
protected final void yycdebug(String s) {
if (0 < yydebug)
yyDebugStream.println(s);
@@ -541,7 +560,12 @@ import java.text.MessageFormat;
/* @@$. */
]b4_location_type[ yyloc;]])[
]b4_push_if([],[[
]b4_define_state[]b4_parse_trace_if([[
]b4_define_state[
]b4_lac_if([[
// Discard the LAC context in case there still is one left from a
// previous invocation.
yylacDiscard("init");]])[
]b4_parse_trace_if([[
yycdebug ("Starting parse");]])[
yyerrstatus_ = 0;
yynerrs = 0;
@@ -635,19 +659,24 @@ b4_dollar_popdef[]dnl
/* If the proper action on seeing token YYTOKEN is to reduce or to
detect an error, take that action. */
yyn += yytoken.getCode();
if (yyn < 0 || YYLAST_ < yyn || yycheck_[yyn] != yytoken.getCode())
if (yyn < 0 || YYLAST_ < yyn || yycheck_[yyn] != yytoken.getCode()) {]b4_lac_if([[
if (!yylacEstablish(yystack, yytoken)) {
label = YYERRLAB;
} else]])[
label = YYDEFAULT;
}
/* <= 0 means reduce or error. */
else if ((yyn = yytable_[yyn]) <= 0)
{
if (yyTableValueIsError (yyn))
if (yyTableValueIsError(yyn)) {
label = YYERRLAB;
else
{
yyn = -yyn;
label = YYREDUCE;
}
}]b4_lac_if([[ else if (!yylacEstablish(yystack, yytoken)) {
label = YYERRLAB;
}]])[ else {
yyn = -yyn;
label = YYREDUCE;
}
}
else
@@ -665,7 +694,8 @@ b4_dollar_popdef[]dnl
--yyerrstatus_;
yystate = yyn;
yystack.push (yystate, yylval]b4_locations_if([, yylloc])[);
yystack.push(yystate, yylval]b4_locations_if([, yylloc])[);]b4_lac_if([[
yylacDiscard("shift");]])[
label = YYNEWSTATE;
}
}
@@ -701,7 +731,7 @@ b4_dollar_popdef[]dnl
++yynerrs;
if (yychar == YYEMPTY_)
yytoken = null;
yyreportSyntaxError(new Context(yystack, yytoken]b4_locations_if([[, yylloc]])[));
yyreportSyntaxError(new Context(this, yystack, yytoken]b4_locations_if([[, yylloc]])[));
}
]b4_locations_if([[
yyerrloc = yylloc;]])[
@@ -784,7 +814,8 @@ b4_dollar_popdef[]dnl
yyloc = yylloc (yystack, 2);
yystack.pop (2);]])[
/* Shift the error token. */]b4_parse_trace_if([[
/* Shift the error token. */]b4_lac_if([[
yylacDiscard("error recovery");]])[]b4_parse_trace_if([[
yySymbolPrint("Shifting", SymbolKind.get(yystos_[yyn]),
yylval]b4_locations_if([, yyloc])[);]])[
@@ -820,7 +851,9 @@ b4_dollar_popdef[]dnl
this.yyn = 0;
this.yylen = 0;
this.yystate = 0;
this.yystack = new YYStack ();
this.yystack = new YYStack();]b4_lac_if([[
this.yylacStack = new Vector<Integer>();
this.yylacEstablished = false;]])[
this.label = YYNEWSTATE;
/* Error handling. */
@@ -881,13 +914,14 @@ b4_dollar_popdef[]dnl
* a syntax error diagnostic.
*/
public static final class Context {
Context (YYStack stack, SymbolKind token]b4_locations_if([[, ]b4_location_type[ loc]])[)
{
Context(]b4_parser_class[ parser, YYStack stack, SymbolKind token]b4_locations_if([[, ]b4_location_type[ loc]])[) {
yyparser = parser;
yystack = stack;
yytoken = token;]b4_locations_if([[
yylocation = loc;]])[
}
private ]b4_parser_class[ yyparser;
private YYStack yystack;
@@ -921,7 +955,27 @@ b4_dollar_popdef[]dnl
}
int getExpectedTokens(SymbolKind yyarg[], int yyoffset, int yyargn) {
int yycount = yyoffset;
int yycount = yyoffset;]b4_lac_if([b4_parse_trace_if([[
// Execute LAC once. We don't care if it is successful, we
// only do it for the sake of debugging output.
if (!yyparser.yylacEstablished)
yyparser.yylacCheck(yystack, yytoken);
]])[
for (int yyx = 0; yyx < YYNTOKENS_; ++yyx)
{
SymbolKind yysym = SymbolKind.get(yyx);
if (yysym != ]b4_symbol(1, kind)[
&& yysym != ]b4_symbol(2, kind)[
&& yyparser.yylacCheck(yystack, yysym))
{
if (yyarg == null)
yycount += 1;
else if (yycount == yyargn)
return 0;
else
yyarg[yycount++] = yysym;
}
}]], [[
int yyn = yypact_[this.yystack.stateAt(0)];
if (!yyPactValueIsDefault(yyn))
{
@@ -944,13 +998,152 @@ b4_dollar_popdef[]dnl
else
yyarg[yycount++] = SymbolKind.get(yyx);
}
}
}]])[
if (yyarg != null && yycount == yyoffset && yyoffset < yyargn)
yyarg[yycount] = null;
return yycount - yyoffset;
}
}
]b4_lac_if([[
/** Check the lookahead yytoken.
* \returns true iff the token will be eventually shifted.
*/
boolean yylacCheck(YYStack yystack, SymbolKind yytoken)
{
// Logically, the yylacStack's lifetime is confined to this function.
// Clear it, to get rid of potential left-overs from previous call.
yylacStack.clear();
// Reduce until we encounter a shift and thereby accept the token.
yycdebugNnl("LAC: checking lookahead " + yytoken.getName() + ":");
int lacTop = 0;
while (true)
{
int topState = (yylacStack.isEmpty()
? yystack.stateAt(lacTop)
: yylacStack.lastElement());
int yyrule = yypact_[topState];
if (yyPactValueIsDefault(yyrule)
|| (yyrule += yytoken.getCode()) < 0 || YYLAST_ < yyrule
|| yycheck_[yyrule] != yytoken.getCode())
{
// Use the default action.
yyrule = yydefact_[+topState];
if (yyrule == 0) {
yycdebug(" Err");
return false;
}
}
else
{
// Use the action from yytable.
yyrule = yytable_[yyrule];
if (yyTableValueIsError(yyrule)) {
yycdebug(" Err");
return false;
}
if (0 < yyrule) {
yycdebug(" S" + yyrule);
return true;
}
yyrule = -yyrule;
}
// By now we know we have to simulate a reduce.
yycdebugNnl(" R" + (yyrule - 1));
// Pop the corresponding number of values from the stack.
{
int yylen = yyr2_[yyrule];
// First pop from the LAC stack as many tokens as possible.
int lacSize = yylacStack.size();
if (yylen < lacSize) {
yylacStack.setSize(lacSize - yylen);
yylen = 0;
} else if (lacSize != 0) {
yylacStack.clear();
yylen -= lacSize;
}
// Only afterwards look at the main stack.
// We simulate popping elements by incrementing lacTop.
lacTop += yylen;
}
// Keep topState in sync with the updated stack.
topState = (yylacStack.isEmpty()
? yystack.stateAt(lacTop)
: yylacStack.lastElement());
// Push the resulting state of the reduction.
int state = yyLRGotoState(topState, yyr1_[yyrule]);
yycdebugNnl(" G" + state);
yylacStack.add(state);
}
}
/** Establish the initial context if no initial context currently exists.
* \returns true iff the token will be eventually shifted.
*/
boolean yylacEstablish(YYStack yystack, SymbolKind yytoken) {
/* Establish the initial context for the current lookahead if no initial
context is currently established.
We define a context as a snapshot of the parser stacks. We define
the initial context for a lookahead as the context in which the
parser initially examines that lookahead in order to select a
syntactic action. Thus, if the lookahead eventually proves
syntactically unacceptable (possibly in a later context reached via a
series of reductions), the initial context can be used to determine
the exact set of tokens that would be syntactically acceptable in the
lookahead's place. Moreover, it is the context after which any
further semantic actions would be erroneous because they would be
determined by a syntactically unacceptable token.
yylacEstablish should be invoked when a reduction is about to be
performed in an inconsistent state (which, for the purposes of LAC,
includes consistent states that don't know they're consistent because
their default reductions have been disabled).
For parse.lac=full, the implementation of yylacEstablish is as
follows. If no initial context is currently established for the
current lookahead, then check if that lookahead can eventually be
shifted if syntactic actions continue from the current context. */
if (yylacEstablished) {
return true;
} else {
yycdebug("LAC: initial context established for " + yytoken.getName());
yylacEstablished = true;
return yylacCheck(yystack, yytoken);
}
}
/** Discard any previous initial lookahead context because of event.
* \param event the event which caused the lookahead to be discarded.
* Only used for debbuging output. */
void yylacDiscard(String event) {
/* Discard any previous initial lookahead context because of Event,
which may be a lookahead change or an invalidation of the currently
established initial context for the current lookahead.
The most common example of a lookahead change is a shift. An example
of both cases is syntax error recovery. That is, a syntax error
occurs when the lookahead is syntactically erroneous for the
currently established initial context, so error recovery manipulates
the parser stacks to try to find a new initial context in which the
current lookahead is syntactically acceptable. If it fails to find
such a context, it discards the lookahead. */
if (yylacEstablished) {
yycdebug("LAC: initial context discarded due to " + event);
yylacEstablished = false;
}
}
/** The stack for LAC.
* Logically, the yylacStack's lifetime is confined to the function
* yylacCheck. We just store it as a member of this class to hold
* on to the memory and to avoid frequent reallocations.
*/
Vector<Integer> yylacStack;
/** Whether an initial LAC context was established. */
boolean yylacEstablished;
]])[
]b4_parse_error_bmatch(
[detailed\|verbose], [[
private int yysyntaxErrorArguments(Context yyctx, SymbolKind[] yyarg, int yyargn) {

8
examples/java/calc/Calc.y
View File

@@ -23,11 +23,17 @@
%define api.parser.public
%define api.push-pull push
// Customized syntax error messages (see reportSyntaxError)...
%define parse.error custom
%define parse.trace
// ... with locations...
%locations
// ... and accurate list of expected tokens.
%define parse.lac full
%define parse.trace
%code imports {
import java.io.BufferedReader;
import java.io.IOException;