Interpreter

parser.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*Symbol linked list*/
typedef struct Symbol{
	char* identifier;
	int value;
	struct Symbol* next;	
} Symbol;
Symbol* list = NULL;
Symbol* lookup_symbols(char* varn) {
	Symbol* curr = list;
	while(curr)	{
		if(!strcmp(varn,curr->identifier)) return curr;
		curr = curr->next;
	}
	curr = malloc(sizeof(Symbol));
	curr->identifier = varn;
	curr->value = 0;
	curr->next=list;
	list=curr;
}
void print_symbols() {
	Symbol* curr = list;
	while(curr)	{
		printf("%s=\t%d\n",curr->identifier,curr->value);
		curr = curr->next;
	}
}
/*end of Symbol crap*/

typedef void (*action)(char);
struct Context{
	int current_state;
	char buffer[256];
	unsigned char buf_c;
	char operator;
	char* var_name;
	int value;
} Context;

/*Utility methods*/
int in(char* arr, char c){
	int size = strlen(arr),i;
	for(i=0;i<size;i++) if (arr[i] == c) return 1;
	return 0;
}
void clear_buffer(){
	Context.buffer[Context.buf_c] = '\0';
	Context.buf_c=0;
}
void eval() {
	Symbol* variable = lookup_symbols(Context.var_name);
	switch(Context.operator) {
		case '+': variable->value+=Context.value;break;
		case '*': variable->value*=Context.value;break;
		case '/': variable->value/=Context.value;break;
		case '-': variable->value-=Context.value;break;
	}
}
/*end*/

/*State transition methods*/
void write_buf(char a){
	Context.buffer[Context.buf_c]=a;
	Context.buf_c++;
}
void clear_push_to_table(char a){
	clear_buffer();
	Context.var_name = (char*) malloc(strlen((Context.buffer))+1);
	strcpy(Context.var_name,Context.buffer);
	Context.operator = a;
}
void clear_push_to_int(char a) {
	clear_buffer();
	Context.value = atoi(Context.buffer);
	eval();
}
void clear_push_lookup_table(char a) {
	clear_buffer();
	Context.value = lookup_symbols(Context.buffer)->value;
	eval();
}
void noop(char a){}
void explode(char a){
	printf("Explode!\n");
	exit(1);
}
/*state transition methods*/

const unsigned int STATES = 6;
const unsigned int ALPHABET = 5;
action** fun;
unsigned int** delta;
char** alphabet;

void construct_dfa() {
	unsigned int i=0;
	unsigned int alpha,num,op,delim,eq;
	alphabet = (char**)malloc(ALPHABET*(sizeof alphabet));
	alphabet[alpha=i++]="_abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
	alphabet[num=i++]="0123456789";
	alphabet[op=i++]="+-*/";
	alphabet[delim=i++]=";";
	alphabet[eq=i++]="=";
	delta = malloc((STATES+1)*(sizeof delta));
	fun = malloc((STATES+1)*(sizeof fun));
	unsigned int d=ALPHABET*(sizeof(*delta));
	unsigned int f=ALPHABET*(sizeof(*fun));
	for(i=0;i<STATES+1;i++) {
		delta[i] = memset(malloc(d),0,d);
		fun[i] = malloc(f);
		int j=0;
		for(j=0;j<ALPHABET;j++) fun[i][j] = explode;
	}
	delta[1][alpha] = delta[2][alpha] = delta[2][num] = 2;
	delta[2][op] = 3;
	delta[3][eq] = 4;
	delta[4][num] = delta[5][num] = 5;
	delta[4][alpha] = delta[6][alpha] = delta[6][num] = 6;
	delta[5][delim] = delta[6][delim] = 1;
	
	fun[1][alpha] = fun[2][alpha] = fun[2][num] = write_buf;
	fun[2][op] = clear_push_to_table;
	fun[3][eq] = noop;
	fun[4][alpha] = fun[4][num] = fun[5][num] = fun[6][alpha] = fun[6][num] = write_buf;
	fun[5][delim] = clear_push_to_int;
	fun[6][delim] = clear_push_lookup_table;
}
int main() {
	construct_dfa();
	Context.current_state = 1;
	while(1) {
		char t = fgetc(stdin);
		if(t=='\n') break;
		int i=0;
		while(i<ALPHABET && !in(alphabet[i],t))	i++;
		printf("%d -'%c'-> %d\n",Context.current_state,t,delta[Context.current_state][i]);
		(*(fun[Context.current_state][i]))(t);
		Context.current_state = delta[Context.current_state][i];
	}
	print_symbols();
	int i;
	int j;
	for(i=0;i<6;i++) {
		for(j=0;j<5;j++) printf(" %d",delta[i][j]);
		printf("\n");
	}
}