simple calculator

.gitignore

@@ -50,3 +50,8 @@ modules.order
 Module.symvers
 Mkfile.old
 dkms.conf
+
+y.tab.h
+y.tab.c
+lex.yy.c
+bin/*

Makefile

@@ -0,0 +1,4 @@
+comp:
+	lex src/lex.l
+	yacc -d src/grammar.y
+	gcc -o bin/main y.tab.c lex.yy.c

src/grammar.y

@@ -0,0 +1,52 @@
+%{
+#include <stdio.h>
+#include <stdlib.h>
+
+int yylex();
+int yyerror(const char *s);
+%}
+
+%union {
+    double double_value;
+}
+
+%token <double_value> DOUBLE_LITERAL
+%token CR LP RP
+%left ADD SUB
+%left MUL DIV
+
+%type <double_value> expr
+
+%%
+stmt_list:
+          stmt
+        | stmt_list stmt
+        ;
+
+stmt:
+     expr CR {
+         printf(">>%lf\n", $1);
+     }
+
+expr:
+           DOUBLE_LITERAL { $$ = $1; }
+         | expr ADD expr  { $$ = $1 + $3; }
+         | expr SUB expr  { $$ = $1 - $3; }
+         | expr MUL expr  { $$ = $1 * $3; }
+         | expr DIV expr  { $$ = $1 / $3; }
+         | LP expr RP     { $$ = $2; }
+         ;
+%%
+
+int yyerror(char const *str) {
+    extern char *yytext;
+    fprintf(stderr, "parse error near %s\n", yytext);
+    return 0;
+}
+
+int main(void) {
+    if (yyparse()) {
+        exit(1);
+    }
+    return 0;
+}

src/lex.l

@@ -0,0 +1,32 @@
+%{
+#include <stdio.h>
+#include "y.tab.h"
+%}
+
+%%
+"+"  return ADD;
+"-"  return SUB;
+"*"  return MUL;
+"/"  return DIV;
+"("  return LP;
+")"  return RP;
+"\n" return CR;
+
+([1-9][0-9]*)|0|([0-9]+\.[0-9]+) {
+    double val;
+    sscanf(yytext, "%lf", &val);
+    yylval.double_value = val;
+    return DOUBLE_LITERAL;
+}
+
+[ \t] ;
+
+. {
+    fprintf(stderr, "lexical error\n");
+    exit(1);
+}
+%%
+
+int yywrap(void) {
+    return 1;
+}