| 101 | |
| 102 | // Given fragments for a and b, returns fragment for a|b. |
| 103 | private Frag alt(Frag f1, Frag f2) { |
| 104 | // alt of failure is other |
| 105 | if (f1.i == 0) { |
| 106 | return f2; |
| 107 | } |
| 108 | if (f2.i == 0) { |
| 109 | return f1; |
| 110 | } |
| 111 | Frag f = newInst(Inst.ALT); |
| 112 | Inst i = prog.getInst(f.i); |
| 113 | i.out = f1.i; |
| 114 | i.arg = f2.i; |
| 115 | f.out = prog.append(f1.out, f2.out); |
| 116 | f.nullable = f1.nullable || f2.nullable; |
| 117 | return f; |
| 118 | } |
| 119 | |
| 120 | // loop returns the fragment for the main loop of a plus or star. |
| 121 | // For plus, it can be used directly. with f1.i as the entry. |