/media/sda-magnetic/david/Dokumente-15-2023-11-22/informatik/compilerbau/pattern-matching/1th-episode/reg14.c

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

struct tree {
    struct tree *l;
    struct tree *r;
    int ch;
};

char expr [] = "(a(((bc(d))lll)de(faaa)))zzz";
int i = 0;

char gettoken () {
    return expr [i++];
}
void tokenback () {
    i--;
}

/*
aaaa
aaaaaa
aaaaaaa
aaaaaaaa()
*/

struct tree *stream ();
struct tree *followed ();
struct tree *compound ();
struct tree *or_operator ();
struct tree *repeat_operator ();

struct tree *or_operator () {
    struct tree *n;
    
    if ((n = malloc (sizeof(struct tree))) == NULL) {
        perror ("Not enough memory");
        exit (1);
    }
    n -> ch = -1;
    n -> l = n -> r = repeat_operator ();
    if (gettoken () == '+') {
        n -> r = repeat_operator ();
    }
    else
        tokenback ();
return n;
}

int repeat_operator () {
    struct tree *n;
    
    if ((n = malloc (sizeof(struct tree))) == NULL) {
        perror ("Not enough memory");
        exit (1);
    }
    n -> ch = -1;
    if (gettoken () == '*') {
        stream ();
    }
    else { 
        tokenback ();
        stream ();
    }
}

int stream () {
    compound ();
    followed ();
}

int followed () {
    int ch = gettoken ();
    if ((ch >= 'a') && (ch <= 'z')) {
        printf ("%c ", ch);
        or_operator ();
    }
    else
        tokenback ();
}

int compound () {
    if (gettoken () == '(') {
        or_operator ();
        if (gettoken () != ')') {
            fprintf (stderr, "fehler klammer vergessen %c %i\n", expr [i], i);
            exit (1);
        }
    }
    else
        tokenback ();
}




int main (void) {
    or_operator ();
}