impl yield from

src/compiler.h

@@ -730,6 +730,19 @@ __SUBSCR_END:
                 ctx()->emit(OP_YIELD_VALUE, BC_NOARG, kw_line);
                 consume_end_stmt();
                 break;
+            case TK("yield from"):
+                if (contexts.size() <= 1) SyntaxError("'yield from' outside function");
+                EXPR_TUPLE(false);
+                // if yield from present, mark the function as generator
+                ctx()->co->is_generator = true;
+                ctx()->emit(OP_GET_ITER, BC_NOARG, kw_line);
+                ctx()->enter_block(FOR_LOOP);
+                ctx()->emit(OP_FOR_ITER, BC_NOARG, BC_KEEPLINE);
+                ctx()->emit(OP_YIELD_VALUE, BC_NOARG, BC_KEEPLINE);
+                ctx()->emit(OP_LOOP_CONTINUE, BC_NOARG, BC_KEEPLINE);
+                ctx()->exit_block();
+                consume_end_stmt();
+                break;
             case TK("return"):
                 if (contexts.size() <= 1) SyntaxError("'return' outside function");
                 if(match_end_stmt()){

src/lexer.h

@@ -9,7 +9,7 @@ namespace pkpy{
 typedef uint8_t TokenIndex;
 
 constexpr const char* kTokens[] = {
-    "is not", "not in",
+    "is not", "not in", "yield from",
     "@eof", "@eol", "@sof",
     "@id", "@num", "@str", "@fstr",
     "@indent", "@dedent",
@@ -231,6 +231,12 @@ struct Lexer {
                     add_token(TK("is not"));
                     return 0;
                 }
+            }else if(name == "yield"){
+                if(strncmp(curr_char, " from", 5) == 0){
+                    curr_char += 5;
+                    add_token(TK("yield from"));
+                    return 0;
+                }
             }
             add_token(kTokenKwMap.at(name));
         } else {

tests/45_yield.py

@@ -28,3 +28,12 @@ assert a[5] == (1,2)
 assert a[6] == (2,0)
 assert a[7] == (2,1)
 assert a[8] == (2,2)
+
+def g():
+    yield from [1, 2, 3]
+
+def f():
+    yield from g()
+
+a = [i for i in f()]
+assert a == [1, 2, 3]