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examples: add an example of a push parser
Add an example to demonstrate the use of push parser. I'm pleasantly surprised: parse.error=detailed works like a charm with push parsers. * examples/c/local.mk, examples/c/pushcalc/Makefile * examples/c/pushcalc/README.md, examples/c/pushcalc/calc.test, * examples/c/pushcalc/calc.y, examples/c/pushcalc/local.mk: New.
This commit is contained in:
Akim Demaille
@@ -37,6 +37,17 @@ recursively. To demonstrate this feature, expressions in parentheses are
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tokenized as strings, and then recursively parsed from the parser. So
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`(((1)+(2))*((3)+(4)))` uses eight parsers, with a depth of four.
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## pushcalc - calculator implemented with a push parser
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All the previous examples are so called "pull parsers": the user invokes the
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parser once, which repeatedly calls the scanner until the input is drained.
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This example demonstrates the "push parsers": the user calls the scanner to
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fetch the next token, passes it to the parser, and repeats the operation
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until the input is drained.
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This example is a straightforward conversion of the 'calc' example to the
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push-parser model.
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<!---
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@@ -19,5 +19,6 @@ dist_c_DATA = %D%/README.md
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include %D%/calc/local.mk
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include %D%/lexcalc/local.mk
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include %D%/mfcalc/local.mk
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include %D%/pushcalc/local.mk
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include %D%/reccalc/local.mk
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include %D%/rpcalc/local.mk
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28
examples/c/pushcalc/Makefile
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28
examples/c/pushcalc/Makefile
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@@ -0,0 +1,28 @@
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# This Makefile is designed to be simple and readable. It does not
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# aim at portability. It requires GNU Make.
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BASE = calc
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BISON = bison
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XSLTPROC = xsltproc
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all: $(BASE)
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%.c %.h %.xml %.gv: %.y
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$(BISON) $(BISONFLAGS) --defines --xml --graph=$*.gv -o $*.c $<
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$(BASE): $(BASE).o
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$(CC) $(CFLAGS) -o $@ $^
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run: $(BASE)
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@echo "Type arithmetic expressions. Quit with ctrl-d."
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./$<
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html: $(BASE).html
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%.html: %.xml
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$(XSLTPROC) $(XSLTPROCFLAGS) -o $@ $$($(BISON) --print-datadir)/xslt/xml2xhtml.xsl $<
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CLEANFILES = \
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$(BASE) *.o $(BASE).[ch] $(BASE).output $(BASE).xml $(BASE).html $(BASE).gv
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clean:
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rm -f $(CLEANFILES)
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39
examples/c/pushcalc/README.md
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39
examples/c/pushcalc/README.md
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@@ -0,0 +1,39 @@
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# pushcalc - push parser with Bison
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This directory contains pushcalc, the traditional calculator, implemented as
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a push parser.
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Traditionally Bison is used to create so called "pull parsers": the user
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invokes the parser once, which repeatedly calls (pulls) the scanner until
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the input is drained.
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This example demonstrates the "push parsers": the user calls scanner to
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fetch the next token, passes (pushes) it to the parser, and repeats the
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operation until the input is drained.
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This example is a straightforward conversion of the 'calc' example to the
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push-parser model.
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<!---
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Local Variables:
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fill-column: 76
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ispell-dictionary: "american"
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End:
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Copyright (C) 2020 Free Software Foundation, Inc.
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This file is part of Bison, the GNU Compiler Compiler.
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This program is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program. If not, see <http://www.gnu.org/licenses/>.
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--->
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42
examples/c/pushcalc/calc.test
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42
examples/c/pushcalc/calc.test
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@@ -0,0 +1,42 @@
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#! /bin/sh
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# Copyright (C) 2020 Free Software Foundation, Inc.
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#
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# This program is free software: you can redistribute it and/or modify
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# it under the terms of the GNU General Public License as published by
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# the Free Software Foundation, either version 3 of the License, or
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# (at your option) any later version.
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#
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# This program is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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# GNU General Public License for more details.
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#
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# You should have received a copy of the GNU General Public License
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# along with this program. If not, see <http://www.gnu.org/licenses/>.
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cat >input <<EOF
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1+2*3
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EOF
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run 0 7
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cat >input <<EOF
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1 - 2 - 3
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EOF
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run 0 -4
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cat >input <<EOF
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8 / 2 / 2
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EOF
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run 0 2
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cat >input <<EOF
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(1+2) * 3
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EOF
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run 0 9
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run -noerr 0 9 -p
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cat >input <<EOF
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1++2
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EOF
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run 0 "err: syntax error, unexpected '+', expecting number or '('"
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114
examples/c/pushcalc/calc.y
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114
examples/c/pushcalc/calc.y
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@@ -0,0 +1,114 @@
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%code top {
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#include <ctype.h> /* isdigit. */
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#include <stdbool.h>
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#include <stdio.h> /* For printf, etc. */
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#include <string.h> /* strcmp. */
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}
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%code {
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int yylex (YYSTYPE *yylval);
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void yyerror (char const *);
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}
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%define api.header.include {"calc.h"}
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/* Generate YYSTYPE from the types used in %token and %type. */
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%define api.value.type union
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%token <double> NUM "number"
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%type <double> expr term fact
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/* Don't share global variables between the scanner and the parser. */
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%define api.pure full
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/* Generate a push parser. */
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%define api.push-pull push
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/* Nice error messages with details. */
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%define parse.error detailed
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/* Generate the parser description file (calc.output). */
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%verbose
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/* Enable run-time traces (yydebug). */
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%define parse.trace
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/* Formatting semantic values in debug traces. */
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%printer { fprintf (yyo, "%g", $$); } <double>;
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%% /* The grammar follows. */
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input:
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%empty
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| input line
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;
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line:
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'\n'
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| expr '\n' { printf ("%.10g\n", $1); }
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| error '\n' { yyerrok; }
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;
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expr:
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expr '+' term { $$ = $1 + $3; }
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| expr '-' term { $$ = $1 - $3; }
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| term
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;
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term:
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term '*' fact { $$ = $1 * $3; }
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| term '/' fact { $$ = $1 / $3; }
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| fact
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;
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fact:
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"number"
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| '(' expr ')' { $$ = $expr; }
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;
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%%
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int
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yylex (YYSTYPE *yylval)
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{
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int c;
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/* Ignore white space, get first nonwhite character. */
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while ((c = getchar ()) == ' ' || c == '\t')
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continue;
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if (c == EOF)
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return 0;
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/* Char starts a number => parse the number. */
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if (c == '.' || isdigit (c))
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{
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ungetc (c, stdin);
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scanf ("%lf", &yylval->NUM);
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return NUM;
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}
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/* Any other character is a token by itself. */
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return c;
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}
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/* Called by yyparse on error. */
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void
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yyerror (char const *s)
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{
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fprintf (stderr, "%s\n", s);
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}
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int
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main (int argc, char const* argv[])
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{
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/* Enable parse traces on option -p. */
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for (int i = 1; i < argc; ++i)
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if (!strcmp (argv[i], "-p"))
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yydebug = 1;
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int status;
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yypstate *ps = yypstate_new ();
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do {
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YYSTYPE lval;
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status = yypush_parse (ps, yylex (&lval), &lval);
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} while (status == YYPUSH_MORE);
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yypstate_delete (ps);
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return status;
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}
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33
examples/c/pushcalc/local.mk
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33
examples/c/pushcalc/local.mk
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@@ -0,0 +1,33 @@
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## Copyright (C) 2020 Free Software Foundation, Inc.
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##
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## This program is free software: you can redistribute it and/or modify
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## it under the terms of the GNU General Public License as published by
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## the Free Software Foundation, either version 3 of the License, or
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## (at your option) any later version.
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##
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## This program is distributed in the hope that it will be useful,
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## but WITHOUT ANY WARRANTY; without even the implied warranty of
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## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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## GNU General Public License for more details.
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##
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## You should have received a copy of the GNU General Public License
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## along with this program. If not, see <http://www.gnu.org/licenses/>.
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pushcalcdir = $(docdir)/%D%
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## ------ ##
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## Calc. ##
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## ------ ##
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check_PROGRAMS += %D%/calc
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TESTS += %D%/calc.test
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EXTRA_DIST += %D%/calc.test
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nodist_%C%_calc_SOURCES = %D%/calc.y
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%D%/calc.c: $(dependencies)
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# Don't use gnulib's system headers.
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%C%_calc_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
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dist_pushcalc_DATA = %D%/calc.y %D%/Makefile %D%/README.md
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CLEANFILES += %D%/calc.[ch] %D%/calc.output
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CLEANDIRS += %D%/*.dSYM
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