E: T
T: T { '+' F } | F
F: F { '*' I } | I
I: <identifier>
یک تجزیهکنندهٔ بازگشتی دنباله ساده میتواند بسیار شبیه به یک تجزیهکنندهٔ بازگشتی تنزلی نوشته شود. الگوریتم معمول برای تجزیهٔ یک دستور زبان مانند دستور زبان بالا با استفاده از یک درخت نحو انتزاعی(AST) بدین شکل است:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>
enum node_type
{
NODE_NUMBER,
NODE_OPERATOR,
NODE_IDENTIFIER,
NODE_MUL,
NODE_ADD
};
typedef struct _exptree exptree;
struct _exptree {
int val;
char* token;
int line_number;
exptree *left;
exptree *right;
};
struct _lexval {
int ival;
char *sval;
int line;
enum node_type typ;
} lexval;
int line_number = 0;
FILE *fs,*fd;
exptree *parse_e(void);
exptree *parse_t(void);
exptree *parse_f(void);
exptree *parse_i(void);
void next_token(){
while (1){
int t;
char *buff;
t = fgetc(fs);
//printf("after getchar = %d\n",t);
if (t == ' ' || t == '\t' || t=='\n'){
//printf("white space\n"); /* ignore whitespace */
}
else if (t == '\n')
{
line_number++;
//printf("line = %i\n",line_number);
return;
}
else if(t == EOF){
return;
}
else if(isdigit(t))
{
//ungetc (t, stdin);
fseek(fs,ftell(fs)-1,SEEK_SET);
fscanf (fs,"%d", &lexval.ival);
//printf("in lexer ival = %d\n",lexval.ival);
lexval.sval = "";
lexval.line = line_number;
lexval.typ = NODE_NUMBER;
return;
} else if (t == '*'){
//printf("lexer mul\n");
//ungetc (t, stdin);
//scanf ("%s", buff);
lexval.sval = "*";
//printf("in lexer ival = %s\n",lexval.sval);
lexval.line = line_number;
lexval.typ = NODE_MUL;
return;
} else if (t == '+'){
//printf("lexer add\n");
//ungetc (t, stdin);
//scanf ("%s0", buff);
lexval.sval = "+";
//printf("in lexer ival = %s\n",lexval.sval);
lexval.line = line_number;
lexval.typ = NODE_ADD;
return;
}
}
}
exptree* alloc_tree(){
return (exptree *) malloc(sizeof(exptree));
}
exptree *parse_e(void)
{
//printf("in e ival = %d\n",lexval.ival);
return parse_t();
}
exptree *parse_t(void)
{
//printf("in t\n");
//printf("in t ival = %d\n",lexval.ival);
exptree *first_f = parse_f();
while(lexval.typ == NODE_ADD) {
//printf("in t loop\n");
exptree *replace_tree = alloc_tree();
replace_tree->token = lexval.sval;
replace_tree->left = first_f;
//printf("in t loop begin next_token\n");
next_token();
//printf("parse_t = %c\n",replace_tree->token);
replace_tree->right = parse_f();
replace_tree->val = replace_tree->left->val + replace_tree->right->val;
printf("hasil t = %d\n",replace_tree->val);
first_f = replace_tree;
}
return first_f;
}
exptree *parse_f(void)
{
//printf("in f\n");
//printf("in f ival = %d\n",lexval.ival);
exptree *first_i = parse_i();
//printf("before f loop\n");
while(lexval.typ == NODE_MUL) {
//printf("in f loop\n");
exptree *replace_tree = alloc_tree();
replace_tree->token = lexval.sval;
replace_tree->left = first_i;
//printf("in f loop begin next_token\n");
next_token();
//printf("parse_f = %c\n",replace_tree->token);
replace_tree->right = parse_i();
replace_tree->val = replace_tree->left->val * replace_tree->right->val;
printf("hasil f = %d\n",replace_tree->val);
first_i = replace_tree;
}
//printf("about to exit from f\n");
return first_i;
}
exptree *parse_i(void)
{
//printf("in i\n");
exptree *i = alloc_tree();
i->left = i->right = NULL;
i->val = lexval.ival;
//printf("in i ival = %d\n",lexval.ival);
//printf("in i = %d\n",i->val);
next_token();
//printf("parse_i = %c\n",i->token);
return i;
}
int main( int argc, char** argv){
if(argc != 2) return 1;
fs = fopen(argv[1], "r");
if (fs == NULL) {
perror("Failed to open file ");
}
//char * = strcat(
fd = fopen (strcat(argv[1],".c"),"w");
if (fd == NULL) {
perror("Failed to open file ");
}
char *template = "#include <stdio.h>\n#include <stdlib.h>\n#include <string.h>\n#include <ctype.h>\n#include <sys/types.h>\nvoid main(){\n";
fputs(template,fd);
char *buffer = malloc(35);
next_token();
exptree *temp = parse_e();
printf("hasil akhir = %d\n",temp->val);
snprintf(buffer, 30, "printf(\"hasil = %d\\n\");\n", temp->val);
fputs(buffer,fd);
fputs("}",fd);
fclose(fs);
fclose(fd);
char *substr = strdup(argv[1]);
char * pch;
pch = strstr(substr,".lol");
strncpy(pch,"\0",1);
snprintf(buffer, 30, "gcc -o %s %s", substr,argv[1]);
system(buffer);
return 0;
}
