dcl

dcl.c

/*
 * My 'dcl' implementation of <the C programming language> chap 5.12.
 * Slightly different from the given implementation.
 *
 * Using left recursion elimination to expand 'dirdcl':
 * dcl    -> optional *'s dirdcl
 * dirdcl -> name
 *         | (dcl)
 *         | dirdcl()
 *         | dirdcl[optional size]
 *
 *      V
 *
 * dcl     -> optional *'s dirdcl
 * dirdcl  -> name dirdcl2
 *          | (dcl) dirdcl2
 * dirdcl2 -> () dirdcl
 *          | [optional size] dirdcl
 *          | \epsilon
 *
 * Usage:
 *  cc dcl.c -o dcl
 *  echo 'int (*(*x())[])()' | ./dcl
 *
 * Author: Senran Zhang
 * Date: Jun. 26, 2019
 */

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

static
char cur = ' ';

static
char tok_str[512];

static
char tok_type;

static
void gettok()
{
	while (isspace(cur))
		cur = getchar();
	if (isalpha(cur) || cur == '_') {
		int i = 0;
		do {
			tok_str[i++] = cur;
			cur = getchar();
		} while (isalnum(cur) || cur == '_');
		tok_str[i] = 0;
		tok_type = -2;
		return;
	}
	if (isdigit(cur)) {
		int i = 0;
		do {
			tok_str[i++] = cur;
			cur = getchar();
		} while (isdigit(cur));
		tok_str[i] = 0;
		tok_type = -3;
		return;
	}
	tok_type = cur;
	cur = getchar();
}

static void dcl();
static void dirdcl();

static
void dcl()
{
	int ns = 0;
	while (tok_type == '*') {
		ns++;
		gettok();
	}
	dirdcl();
	while (ns--)
		printf(" pointer to");
}

static
void dirdcl2()
{
	if (tok_type == '[') {
		fputs(" array[", stdout);
		gettok();
		if (tok_type == -2 || tok_type == -3) {
			fputs(tok_str, stdout);
			gettok();
		}
		if (tok_type != ']') {
			fprintf(stderr, "\nUnclosed branket!\n");
			exit(-1);
		}
		fputs("] of", stdout);
	} else if (tok_type == '(') {
		// TODO: add arguments
		gettok();
		if (tok_type != ')') {
			fprintf(stderr, "\nUnclosed parenthese!\n");
			exit(-1);
		}
		fputs(" function returning", stdout);
	} else {
		fprintf(stderr, "\nInvalid syntax! line %d\n", __LINE__);
		exit(-1);
	}
	gettok();
	if (tok_type != EOF && tok_type != ')') {
		dirdcl();
	}
}

static
void dirdcl()
{
	if (tok_type == '(') {
		gettok();
		dcl();
		if (tok_type != ')') {
			fprintf(stderr, "\nUnclosed parenthese!\n");
			exit(-1);
		}
	} else if (tok_type == -2) {
		fputs(tok_str, stdout);
		putchar(':');
	} else {
		fprintf(stderr, "\nInvalid syntax! line %d\n", __LINE__);
		exit(-1);
	}
	gettok();
	if (tok_type == '(' || tok_type == '[') {
		dirdcl2();
	}
}

int main()
{
	gettok();
	if (tok_type != -2) {
		fprintf(stderr, "\nDatetype Expected!\n");
		exit(-1);
	}
	const char *ret_type = strdup(tok_str);
	gettok();
	dcl();
	putchar(' ');
	puts(ret_type);
}