Recently I've had to write Brainfuck interpreter using Flex and Biso
Brainfuck.l:
/*geditBrainfuck.y
*/
%{
#include <stdlib.h>
#include <stdio.h>
#include "Node.h"
#include "Brainfuck.h"
%}
%%
[\-\[\]\<\>\+\,\.] { return *yytext; }
[\n] { return END; }
.
%%
/*main() { printf("%d", yylex());}*/
/*gedit
*/
%{
#include <stdlib.h>
#include <stdio.h>
#include "Node.h"
#define MAX_MEMORY 30000
#define INNER 0
#define LOOP 1
unsigned static char tab[MAX_MEMORY]; //static, no need to initialize with zero
int pointer;
Node *parse(int op, Node *prev, Node *next);
void delete_node(Node *p);
void yyerror(char *string);
int execute(Node *p);
int yylex(void);
%}
%union{
Node *nodePointer;
}
%type <nodePointer> instruction instruction_list
%token END
%%
program:
instruction_list END { execute($1); delete_node($1); exit(0); }
;
instruction_list:
instruction { $$ = $1; }
| instruction_list instruction { $$ = parse(INNER, $1, $2); }
;
instruction:
'<' { $$ = parse('<', NULL, NULL); }
| '>' { $$ = parse('>', NULL, NULL); }
| ',' { $$ = parse(',', NULL, NULL); }
| '.' { $$ = parse('.', NULL, NULL); }
| '+' { $$ = parse('+', NULL, NULL); }
| '-' { $$ = parse('-', NULL, NULL); }
| '[' instruction_list ']' { $$ = parse(LOOP, $2, NULL); }
;
%%
Node *parse(int op, Node *prev, Node *next) {
Node *node;
if ((node = (Node *)malloc(sizeof(Node))) == NULL)
yyerror("Out of memory.");
node->op = op;
node->prev = prev;
node->next = next;
return node;
}
void delete_node(Node *p){
if (p == NULL)
return;
delete_node(p->next);
delete_node(p->prev);
free(p);
}
void yyerror(char *string){
printf("%s\n", string);
}
int execute(Node *p){
if (p == NULL)
return 0;
switch(p->op){
case '>':
pointer++;
if (pointer >= MAX_MEMORY) {
yyerror("Pointer out of bounds.");
return -1;
}
return 0;
case '<':
pointer--;
if (pointer < 0){
yyerror("Pointer out of bounds.");
return -1;
}
return 0;
case '+':
tab[pointer]++; return 0;
case '-':
tab[pointer]--; return 0;
case '.':
putchar(tab[pointer]); return 0;
case ',':
tab[pointer] = getchar(); return 0;
case LOOP:
while (tab[pointer])
execute(p->prev);
execute(p->next);
return 0;
case INNER:
execute(p->prev);
execute(p->next);
return 0;
}
return -1;
}
int main()
{
pointer = 0;
yyparse();
}
Node.h
/*
*/
typedef struct Node{
int op;
void *prev;
void *next;
}Node;
Makefile:
OBJS = Brainfuck.y.o Brainfuck.l.o
GCC = gcc
Brainfuck: $(OBJS)
@echo " >> Compile and Link"
$(GCC) -o Brainfuck $(OBJS) -lfl
Brainfuck.l.o: Brainfuck.l.c
@echo " >> Compile Flex generated file"
$(GCC) -c Brainfuck.l.c -o Brainfuck.l.o
Brainfuck.l.c: Brainfuck.l
@echo " >> Use Flex"
flex Brainfuck.l
mv lex.yy.c Brainfuck.l.c
Brainfuck.y.o: Brainfuck.y.c
@echo " >> Compile Bison generated file"
$(GCC) -c Brainfuck.y.c -o Brainfuck.y.o
Brainfuck.y.c: Brainfuck.y
@echo " >> Use Bison"
bison -d Brainfuck.y
@echo " >> Rename results"
mv Brainfuck.tab.h Brainfuck.h
mv Brainfuck.tab.c Brainfuck.y.c
Brainfuck.y.o: Node.h
clean:
rm *.o Brainfuck.h Brainfuck.l.c Brainfuck.y.c Brainfuck
