CS118 Programming Languages

Lecture 8

Contents

1. Recursive Parsing
2. Assignments

Recursive Parsing

Summary: Start with a regular expression grammar where all left recursion is replaced with Kleene star. Each Kleene star is replaced by a while loop. Lookahead may be needed to decide to stop the while loop. The output is the shift/reduce sequence.

Example: suppose you have the little 4 rule grammar

P = E;                      r1
E = E + T;                  r2
E = T;                      r3
T = 1;                      r4

P = E
E = T (+ T)*
T = 1

static int tok;
void P(void) {E(); reduce(r1);}
void E(void) {
  T(); reduce(r3);
  while(tok == PLUS) {
    shift(tok); tok=nexttok();
    T(); reduce(r2);
  }
}
void T(void) {
  if (tok == ONE) {
    shift(tok); tok=nexttok();
  } else error();
  reduce(r4);
}