first commit

.gitignore

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+/l
+*.o
+lex.yy.c
+y.tab.[ch]

Makefile

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+CC ?=     cc
+CFLAGS=   -Wfatal-errors -Wall -Wextra
+LDFLAGS=  -s
+
+all: l
+
+l: l.o y.tab.c y.tab.h lex.yy.c
+	cc lex.yy.c y.tab.c -o $@
+lex.yy.c: l.l
+	lex $^
+y.tab.c: l.y
+	yacc -d $^
+
+%.o: %.c
+	$(CC) -c $^ $(CFLAGS) $(LDFLAGS)
+clean:
+	$(RM) l y.tab.c y.tab.h lex.yy.c

l.l

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+%option noyywrap
+
+%{
+#include <stdio.h>
+#define YY_DECL int yylex()
+#include "y.tab.h"
+%}
+
+%%
+
+[ \t]			; // ignore all whitespace
+[0-9]+ {yylval = atoi(yytext); return T_INT;}
+\n	{return T_NEWLINE;}
+"+"	{return T_PLUS;}
+"-"	{return T_MINUS;}
+"*"	{return T_MULTIPLY;}
+"/"	{return T_DIVIDE;}
+"("	{return T_LEFT;}
+")"	{return T_RIGHT;}
+"exit"	{return T_QUIT;}
+"quit"	{return T_QUIT;}
+
+%%

l.y

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+%{
+#include <stdio.h>
+#include <stdlib.h>
+
+extern int yylex();
+extern int yyparse();
+extern FILE* yyin;
+
+void yyerror(const char* s);
+%}
+
+%token T_PLUS T_MINUS T_MULTIPLY T_DIVIDE T_LEFT T_RIGHT
+%token T_NEWLINE T_QUIT T_INT
+%start translation_unit
+
+%%
+
+translation_unit: line
+				| translation_unit line
+;
+
+line: T_INT T_NEWLINE {printf("%d\n",$1);}
+;
+
+%%
+
+int main()
+{
+	yyin = stdin;
+	do yyparse();
+	while(!feof(yyin));
+}
+
+void yyerror(const char*s)
+{
+	fprintf(stderr, "Parse error: %s\n", s);
+	exit(1);
+}
+