/* lpard.c: parser for simple lisp, early scan
 * grammar:  sexpr  --->  alphanum   |   "("  tail
 *           tail   --->  ")"        |    sexpr    tail    */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void sexpr(void);
void tail(void);
char gettoken(void);
void err(int);
void nestBlanks(int n);
void enter(char* s);
void leave(char* s);
char tok; /* the next token */
int debug = 1; /* produce debug output */
int nest; /* used for debug output */

void main(void) {
    tok = gettoken();
    sexpr();
}
/* sexpr: recognize a lisp s-expression */
void sexpr(void) {
                            if (debug) enter("sexpr");
    if (isalnum(tok))
        tok = gettoken();
    else if (tok == '(') {
        tok = gettoken();
        tail();
    }
    else err(0);
                            if (debug) leave("sexpr");
}
/* tail: recognize tail end of a lisp s-expression */
void tail (void) {
                            if (debug) enter("tail");
    if (tok == ')')
        tok = gettoken();
    else {
        sexpr();
        tail();
    }
                            if (debug) leave("tail");
}
four06% lpares
(a (b c) d)
+Enter sexpr, 	 tok: (
| +Enter tail, 	 tok: a
| | +Enter sexpr, 	 tok: a
| | +Leave sexpr, 	 tok: (
| | +Enter tail, 	 tok: (
| | | +Enter sexpr, 	 tok: (
| | | | +Enter tail, 	 tok: b
| | | | | +Enter sexpr, 	 tok: b
| | | | | +Leave sexpr, 	 tok: c
| | | | | +Enter tail, 	 tok: c
| | | | | | +Enter sexpr, 	 tok: c
| | | | | | +Leave sexpr, 	 tok: )
| | | | | | +Enter tail, 	 tok: )
| | | | | | +Leave tail, 	 tok: d
| | | | | +Leave tail, 	 tok: d
| | | | +Leave tail, 	 tok: d
| | | +Leave sexpr, 	 tok: d
| | | +Enter tail, 	 tok: d
| | | | +Enter sexpr, 	 tok: d
| | | | +Leave sexpr, 	 tok: )
| | | | +Enter tail, 	 tok: )         CTRL-D entered
| | | | +Leave tail, 	 tok: 
| | | +Leave tail, 	 tok: 
| | +Leave tail, 	 tok: 
| +Leave tail, 	 tok: 
+Leave sexpr, 	 tok: 
/* lpard.c: parser for simple lisp, late scan
 * grammar:  sexpr  --->  alphanum   |   "("  tail
 *           tail   --->  ")"        |    sexpr    tail     */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void sexpr(void);
void tail(void);
char gettoken(void);
void err(int);
void nestBlanks(int n);
void enter(char* s);
void leave(char* s);
char tok; /* the next token */
int debug = 1; /* produce debug output */
int nest; /* used for debug output */

void main(void) {
    tok = gettoken();
    sexpr();
}
/* sexpr: recognize a lisp s-expression */
void sexpr(void) {
                            if (debug) enter("sexpr");
    if (isalnum(tok))
        ; /* nothing for now */
    else if (tok == '(')
        tail();
    else err(0);
                            if (debug) leave("sexpr");
}
/* tail: recognize tail end of a lisp s-expression */
void tail (void) {
                            if (debug) enter("tail");
    tok = gettoken();
    if (tok == ')')
        ; /* nothing for now */
    else {
        sexpr();
        tail();
    }
                            if (debug) leave("tail");
}

four06% lpard
(a (b c) d)
+Enter sexpr, 	 tok: (
| +Enter tail, 	 tok: (
| | +Enter sexpr, 	 tok: a
| | +Leave sexpr, 	 tok: a
| | +Enter tail, 	 tok: a
| | | +Enter sexpr, 	 tok: (
| | | | +Enter tail, 	 tok: (
| | | | | +Enter sexpr, 	 tok: b
| | | | | +Leave sexpr, 	 tok: b
| | | | | +Enter tail, 	 tok: b
| | | | | | +Enter sexpr, 	 tok: c
| | | | | | +Leave sexpr, 	 tok: c
| | | | | | +Enter tail, 	 tok: c
| | | | | | +Leave tail, 	 tok: )
| | | | | +Leave tail, 	 tok: )
| | | | +Leave tail, 	 tok: )
| | | +Leave sexpr, 	 tok: )
| | | +Enter tail, 	 tok: )
| | | | +Enter sexpr, 	 tok: d
| | | | +Leave sexpr, 	 tok: d
| | | | +Enter tail, 	 tok: d
| | | | +Leave tail, 	 tok: )
| | | +Leave tail, 	 tok: )
| | +Leave tail, 	 tok: )
| +Leave tail, 	 tok: )
+Leave sexpr, 	 tok: )