impl `yield` stmt

src/codeobject.h

@@ -51,6 +51,7 @@ struct CodeBlock {
 struct CodeObject {
     pkpy::shared_ptr<SourceData> src;
     Str name;
+    bool is_generator = false;
 
     CodeObject(pkpy::shared_ptr<SourceData> src, Str name) {
         this->src = src;

src/compiler.h

@@ -849,9 +849,16 @@ __LISTCOMP:
             if (!co()->_is_curr_block_loop()) SyntaxError("'continue' not properly in loop");
             consume_end_stmt();
             emit(OP_LOOP_CONTINUE);
+        } else if (match(TK("yield"))) {
+            if (codes.size() == 1) SyntaxError("'yield' outside function");
+            co()->_rvalue = true;
+            EXPR_TUPLE();
+            co()->_rvalue = false;
+            consume_end_stmt();
+            co()->is_generator = true;
+            emit(OP_YIELD_VALUE, -1, true);
         } else if (match(TK("return"))) {
-            if (codes.size() == 1)
-                SyntaxError("'return' outside function");
+            if (codes.size() == 1) SyntaxError("'return' outside function");
             if(match_end_stmt()){
                 emit(OP_LOAD_NONE);
             }else{

src/iter.h

@@ -11,11 +11,12 @@ public:
         this->current = r.start;
     }
 
-    bool has_next(){
+    inline bool _has_next(){
         return r.step > 0 ? current < r.stop : current > r.stop;
     }
 
     PyVar next(){
+        if(!_has_next()) return nullptr;
         current += r.step;
         return vm->PyInt(current-r.step);
     }
@@ -27,8 +28,10 @@ class ArrayIter : public BaseIter {
     const T* p;
 public:
     ArrayIter(VM* vm, PyVar _ref) : BaseIter(vm, _ref) { p = &OBJ_GET(T, _ref);}
-    bool has_next(){ return index < p->size(); }
-    PyVar next(){ return p->operator[](index++); }
+    PyVar next(){
+        if(index == p->size()) return nullptr;
+        return p->operator[](index++); 
+    }
 };
 
 class StringIter : public BaseIter {
@@ -39,6 +42,31 @@ public:
         str = OBJ_GET(Str, _ref);
     }
 
-    bool has_next(){ return index < str.u8_length(); }
-    PyVar next() { return vm->PyStr(str.u8_getitem(index++)); }
+    PyVar next() {
+        if(index == str.u8_length()) return nullptr;
+        return vm->PyStr(str.u8_getitem(index++));
+    }
 };
+
+class Generator: public BaseIter {
+    std::unique_ptr<Frame> frame;
+    int state; // 0,1,2
+public:
+    Generator(VM* vm, std::unique_ptr<Frame>&& frame)
+        : BaseIter(vm, nullptr), frame(std::move(frame)), state(0) {}
+
+    PyVar next() {
+        if(state == 2) return nullptr;
+        vm->callstack.push(std::move(frame));
+        PyVar ret = vm->_exec();
+        if(ret == vm->_py_op_yield){
+            frame = std::move(vm->callstack.top());
+            vm->callstack.pop();
+            state = 1;
+            return frame->pop_value(vm);
+        }else{
+            state = 2;
+            return nullptr;
+        }
+    }
+};

src/obj.h

@@ -68,7 +68,6 @@ protected:
     PyVar _ref;     // keep a reference to the object so it will not be deleted while iterating
 public:
     virtual PyVar next() = 0;
-    virtual bool has_next() = 0;
     PyVarRef var;
     BaseIter(VM* vm, PyVar _ref) : vm(vm), _ref(_ref) {}
     virtual ~BaseIter() = default;

src/opcodes.h

@@ -68,6 +68,7 @@ OPCODE(DELETE_REF)
 OPCODE(TRY_BLOCK_ENTER)
 OPCODE(TRY_BLOCK_EXIT)
 
+OPCODE(YIELD_VALUE)
 //OPCODE(FAST_INDEX_0)      // a[0]
 //OPCODE(FAST_INDEX_1)      // a[i]
 

src/parser.h

@@ -12,7 +12,7 @@ constexpr const char* kTokens[] = {
     "==", "!=", ">=", "<=",
     "+=", "-=", "*=", "/=", "//=", "%=", "&=", "|=", "^=",
     /** KW_BEGIN **/
-    "class", "import", "as", "def", "lambda", "pass", "del", "from", "with",
+    "class", "import", "as", "def", "lambda", "pass", "del", "from", "with", "yield",
     "None", "in", "is", "and", "or", "not", "True", "False", "global", "try", "except", "finally",
     "goto", "label",      // extended keywords, not available in cpython
     "while", "for", "if", "elif", "else", "break", "continue", "return", "assert", "raise",

tests/_yield.py

@@ -0,0 +1,7 @@
+def f(n):
+    for i in range(n):
+        yield i
+
+a = [i for i in f(6)]
+
+assert a == [0,1,2,3,4,5]