examples: add a simple infix calculator in C

Currently we have no simple example: rpcalc in reverse Polish, mfcalc
has functions, and lexcalc is using lex.

* examples/c/calc/Makefile, examples/c/calc/calc.y,
* examples/c/calc/calc.test, examples/c/calc/local.mk: New.

examples/c/calc/Makefile

@@ -0,0 +1,28 @@
+# This Makefile is designed to be simple and readable.  It does not
+# aim at portability.  It requires GNU Make.
+
+BASE = calc
+BISON = bison
+XSLTPROC = xsltproc
+
+all: $(BASE)
+
+%.c %.h %.xml %.gv: %.y
+	$(BISON) $(BISONFLAGS) --defines --xml --graph=$*.gv -o $*.c $<
+
+$(BASE): $(BASE).o
+	$(CC) $(CFLAGS) -o $@ $^
+
+run: $(BASE)
+	@echo "Type arithmetic expressions.  Quit with ctrl-d."
+	./$<
+
+html: $(BASE).html
+%.html: %.xml
+	$(XSLTPROC) $(XSLTPROCFLAGS) -o $@ $$($(BISON) --print-datadir)/xslt/xml2xhtml.xsl $<
+
+CLEANFILES =									\
+  $(BASE) *.o $(BASE).[ch] $(BASE).output $(BASE).xml $(BASE).html $(BASE).gv
+
+clean:
+	rm -f $(CLEANFILES)

examples/c/calc/README.md

@@ -0,0 +1,28 @@
+# calc - calculator with Bison
+
+This directory contains calc, the traditional example of using Bison to
+build a simple calculator.
+
+<!---
+Local Variables:
+fill-column: 76
+ispell-dictionary: "american"
+End:
+
+Copyright (C) 2019 Free Software Foundation, Inc.
+
+This file is part of Bison, the GNU Compiler Compiler.
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+--->

examples/c/calc/calc.test

@@ -0,0 +1,37 @@
+#! /bin/sh
+
+# Copyright (C) 2019 Free Software Foundation, Inc.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+cat >input <<EOF
+1+2*3
+EOF
+run 0 7
+
+cat >input <<EOF
+1 - 2 - 3
+EOF
+run 0 -4
+
+cat >input <<EOF
+8 / 2 / 2
+EOF
+run 0 2
+
+cat >input <<EOF
+(1+2) * 3
+EOF
+run 0 9
+run -noerr 0 9 -p

examples/c/calc/calc.y

@@ -0,0 +1,93 @@
+%code top {
+  #include <ctype.h>  /* isdigit. */
+  #include <stdio.h>  /* For printf, etc. */
+  #include <string.h> /* strcmp. */
+
+  int yylex (void);
+  void yyerror (char const *);
+}
+
+%define api.value.type union /* Generate YYSTYPE from these types:  */
+%token <double> NUM "number"
+%type  <double> expr term fact
+
+/* Generate the parser description file.  */
+%verbose
+/* Enable run-time traces (yydebug).  */
+%define parse.trace
+
+/* Formatting semantic values.  */
+%printer { fprintf (yyo, "%g", $$); } <double>;
+
+%% /* The grammar follows.  */
+input:
+  %empty
+| input line
+;
+
+line:
+  '\n'
+| expr '\n'  { printf ("%.10g\n", $1); }
+| error '\n' { yyerrok; }
+;
+
+expr:
+  expr '+' term { $$ = $1 + $3; }
+| expr '-' term { $$ = $1 - $3; }
+| term
+;
+
+term:
+  term '*' fact { $$ = $1 * $3; }
+| term '/' fact { $$ = $1 / $3; }
+| fact
+;
+
+fact:
+  "number"
+| '(' expr ')' { $$ = $2; }
+;
+
+%%
+
+int
+yylex (void)
+{
+  int c;
+
+  /* Ignore white space, get first nonwhite character.  */
+  while ((c = getchar ()) == ' ' || c == '\t')
+    continue;
+
+  if (c == EOF)
+    return 0;
+
+  /* Char starts a number => parse the number.         */
+  if (c == '.' || isdigit (c))
+    {
+      ungetc (c, stdin);
+      scanf ("%lf", &yylval.NUM);
+      return NUM;
+    }
+
+  /* Any other character is a token by itself.        */
+  return c;
+}
+
+/* Called by yyparse on error.  */
+void
+yyerror (char const *s)
+{
+  fprintf (stderr, "%s\n", s);
+}
+
+int
+main (int argc, char const* argv[])
+{
+  int i;
+  /* Enable parse traces on option -p.  */
+  for (i = 1; i < argc; ++i)
+    if (!strcmp(argv[i], "-p"))
+      yydebug = 1;
+  return yyparse ();
+}

examples/c/calc/local.mk

@@ -0,0 +1,32 @@
+## Copyright (C) 2019 Free Software Foundation, Inc.
+##
+## This program is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+calcdir = $(docdir)/%D%
+
+## ------ ##
+## Calc.  ##
+## ------ ##
+
+check_PROGRAMS += %D%/calc
+TESTS += %D%/calc.test
+EXTRA_DIST += %D%/calc.test
+%C%_calc_SOURCES = %D%/calc.y
+
+# Don't use gnulib's system headers.
+%C%_calc_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
+
+dist_calc_DATA = %D%/calc.y %D%/Makefile %D%/README.md
+CLEANFILES += %D%/calc %D%/*.o %D%/parse.c %D%/scan.c
+CLEANDIRS += %D%/*.dSYM