interp: fix memory handling of global values

In some cases, the global character of a value was lost, leading to
undefined behaviour. Now a node level field of -1 means that the value
is global, and that it should be accessed from the root data frame.

Fixes #993.

_test/assert0.go

@@ -48,6 +48,14 @@ func main() {
 	bType := reflect.TypeOf(TestStruct{})
 	fmt.Println(bType.Implements(aType))
 
+	// not redundant with the above, because it goes through a slightly different code path.
+	if _, ok := t.(MyWriter); !ok {
+		fmt.Println("TestStruct does not implement MyWriter")
+		return
+	} else {
+		fmt.Println("TestStruct implements MyWriter")
+	}
+
 	t = 42
 	foo, ok := t.(MyWriter)
 	if !ok {
@@ -57,6 +65,12 @@ func main() {
 	}
 	_ = foo
 
+	if _, ok := t.(MyWriter); !ok {
+		fmt.Println("42 does not implement MyWriter")
+	} else {
+		fmt.Println("42 implements MyWriter")
+	}
+
 	var tt interface{}
 	tt = time.Nanosecond
 	var myD MyStringer
@@ -72,6 +86,12 @@ func main() {
 	dType := reflect.TypeOf(time.Nanosecond)
 	fmt.Println(dType.Implements(cType))
 
+	if _, ok := tt.(MyStringer); !ok {
+		fmt.Println("time.Nanosecond does not implement MyStringer")
+	} else {
+		fmt.Println("time.Nanosecond implements MyStringer")
+	}
+
 	tt = 42
 	bar, ok := tt.(MyStringer)
 	if !ok {
@@ -81,6 +101,11 @@ func main() {
 	}
 	_ = bar
 
+	if _, ok := tt.(MyStringer); !ok {
+		fmt.Println("42 does not implement MyStringer")
+	} else {
+		fmt.Println("42 implements MyStringer")
+	}
 }
 
 // Output:
@@ -88,9 +113,13 @@ func main() {
 // 11
 // 11
 // true
+// TestStruct implements MyWriter
+// 42 does not implement MyWriter
 // 42 does not implement MyWriter
 // time.Nanosecond implements MyStringer
 // 1ns
 // 1ns
 // true
+// time.Nanosecond implements MyStringer
+// 42 does not implement MyStringer
 // 42 does not implement MyStringer

_test/assert1.go

@@ -27,6 +27,13 @@ func main() {
 	bType := reflect.TypeOf(time.Nanosecond)
 	fmt.Println(bType.Implements(aType))
 
+	// not redundant with the above, because it goes through a slightly different code path.
+	if _, ok := t.(fmt.Stringer); !ok {
+		fmt.Println("time.Nanosecond does not implement fmt.Stringer")
+		return
+	} else {
+		fmt.Println("time.Nanosecond implements fmt.Stringer")
+	}
 
 	t = 42
 	foo, ok := t.(fmt.Stringer)
@@ -34,9 +41,17 @@ func main() {
 		fmt.Println("42 does not implement fmt.Stringer")
 	} else {
 		fmt.Println("42 implements fmt.Stringer")
+		return
 	}
 	_ = foo
 
+	if _, ok := t.(fmt.Stringer); !ok {
+		fmt.Println("42 does not implement fmt.Stringer")
+	} else {
+		fmt.Println("42 implements fmt.Stringer")
+		return
+	}
+
 	var tt interface{}
 	tt = TestStruct{}
 	ss, ok := tt.(fmt.Stringer)
@@ -49,12 +64,22 @@ func main() {
 	// TODO(mpl): uncomment when fixed
 	// cType := reflect.TypeOf(TestStruct{})
 	// fmt.Println(cType.Implements(aType))
+
+	if _, ok := tt.(fmt.Stringer); !ok {
+		fmt.Println("TestStuct does not implement fmt.Stringer")
+		return
+	} else {
+		fmt.Println("TestStuct implements fmt.Stringer")
+	}
 }
 
 // Output:
 // 1ns
 // 1ns
 // true
+// time.Nanosecond implements fmt.Stringer
+// 42 does not implement fmt.Stringer
 // 42 does not implement fmt.Stringer
 // hello world
 // hello world
+// TestStuct implements fmt.Stringer

_test/composite15.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"fmt"
+)
+
+func interfaceAsInts() {
+	var a interface{}
+	b := 2
+	c := 3
+	a = []int{b, c}
+
+	d, ok := a.([]int)
+	if !ok {
+		println("nope")
+		return
+	}
+
+	for _, v := range d {
+		fmt.Println(v)
+	}
+}
+
+func interfaceAsInterfaces() {
+	var a, b, c interface{}
+	b = 2
+	c = 3
+	a = []interface{}{b, c}
+
+	d, ok := a.([]interface{})
+	if !ok {
+		println("nope")
+		return
+	}
+
+	for _, v := range d {
+		fmt.Println(v)
+	}
+}
+
+func main() {
+	interfaceAsInts()
+	interfaceAsInterfaces()
+}
+
+// Output:
+// 2
+// 3
+// 2
+// 3

_test/composite16.go

@@ -0,0 +1,16 @@
+package main
+
+import (
+	"fmt"
+	"net/url"
+)
+
+func main() {
+	body := url.Values{
+		"Action": {"none"},
+	}
+	fmt.Println(body)
+}
+
+// Output:
+// map[Action:[none]]

_test/interface47.go

@@ -0,0 +1,32 @@
+package main
+
+type Doer interface {
+	Do() error
+}
+
+type T struct {
+	Name string
+}
+
+func (t *T) Do() error { println("in do"); return nil }
+
+func f() (Doer, error) { return &T{"truc"}, nil }
+
+type Ev struct {
+	doer func() (Doer, error)
+}
+
+func (e *Ev) do() {
+	d, _ := e.doer()
+	d.Do()
+}
+
+func main() {
+	e := &Ev{f}
+	println(e != nil)
+	e.do()
+}
+
+// Output:
+// true
+// in do

_test/issue-993.go

@@ -0,0 +1,15 @@
+package main
+
+var m map[string]int64
+
+func initVar() {
+	m = make(map[string]int64)
+}
+
+func main() {
+	initVar()
+	println(len(m))
+}
+
+// Output:
+// 0

_test/var15.go

@@ -0,0 +1,15 @@
+package main
+
+var a int = 2
+
+func inca() {
+	a = a + 1
+}
+
+func main() {
+	inca()
+	println(a)
+}
+
+// Output:
+// 3

interp/cfg.go

@@ -288,8 +288,12 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				// Get type from ancestor (implicit type)
 				if n.anc.kind == keyValueExpr && n == n.anc.child[0] {
 					n.typ = n.anc.typ.key
-				} else if n.anc.typ != nil {
-					n.typ = n.anc.typ.val
+				} else if atyp := n.anc.typ; atyp != nil {
+					if atyp.cat == valueT {
+						n.typ = &itype{cat: valueT, rtype: atyp.rtype.Elem()}
+					} else {
+						n.typ = atyp.val
+					}
 				}
 				if n.typ == nil {
 					err = n.cfgErrorf("undefined type")
@@ -607,7 +611,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				}
 				if n.anc.kind == constDecl {
 					n.gen = nop
-					n.findex = -1
+					n.findex = notInFrame
 					if sym, _, ok := sc.lookup(dest.ident); ok {
 						sym.kind = constSym
 					}
@@ -648,7 +652,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				if n.child[0].ident == "_" {
 					lc.gen = typeAssertStatus
 				} else {
-					lc.gen = typeAssert2
+					lc.gen = typeAssertLong
 				}
 				n.gen = nop
 			case unaryExpr:
@@ -713,7 +717,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				// This operation involved constants, and the result is already computed
 				// by constOp and available in n.rval. Nothing else to do at execution.
 				n.gen = nop
-				n.findex = -1
+				n.findex = notInFrame
 			case n.anc.kind == assignStmt && n.anc.action == aAssign:
 				// To avoid a copy in frame, if the result is to be assigned, store it directly
 				// at the frame location of destination.
@@ -854,7 +858,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				}
 				switch {
 				case n.typ.cat == builtinT:
-					n.findex = -1
+					n.findex = notInFrame
 					n.val = nil
 				case n.anc.kind == returnStmt:
 					// Store result directly to frame output location, to avoid a frame copy.
@@ -896,7 +900,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 					n.rval = c1.rval
 				case c1.rval.IsValid() && isConstType(c0.typ):
 					n.gen = nop
-					n.findex = -1
+					n.findex = notInFrame
 					n.typ = c0.typ
 					if c, ok := c1.rval.Interface().(constant.Value); ok {
 						i, _ := constant.Int64Val(constant.ToInt(c))
@@ -959,7 +963,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 						}
 					}
 				} else {
-					n.findex = -1
+					n.findex = notInFrame
 				}
 			}
 
@@ -1040,7 +1044,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 		case fileStmt:
 			wireChild(n, varDecl)
 			sc = sc.pop()
-			n.findex = -1
+			n.findex = notInFrame
 
 		case forStmt0: // for {}
 			body := n.child[0]
@@ -1498,6 +1502,9 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				// Resolve source package symbol
 				if sym, ok := interp.srcPkg[pkg][name]; ok {
 					n.findex = sym.index
+					if sym.global {
+						n.level = globalFrame
+					}
 					n.val = sym.node
 					n.gen = nop
 					n.action = aGetSym
@@ -1512,7 +1519,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				if n.child[0].isType(sc) {
 					// Handle method as a function with receiver in 1st argument
 					n.val = m
-					n.findex = -1
+					n.findex = notInFrame
 					n.gen = nop
 					n.typ = &itype{}
 					*n.typ = *m.typ
@@ -1825,7 +1832,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 			switch {
 			case n.rval.IsValid():
 				n.gen = nop
-				n.findex = -1
+				n.findex = notInFrame
 			case n.anc.kind == assignStmt && n.anc.action == aAssign:
 				dest := n.anc.child[childPos(n)-n.anc.nright]
 				n.typ = dest.typ
@@ -1852,6 +1859,7 @@ func (interp *Interpreter) cfg(root *node, importPath string) ([]*node, error) {
 				if sc.global {
 					// Global object allocation is already performed in GTA.
 					index = sc.sym[c.ident].index
+					c.level = globalFrame
 				} else {
 					index = sc.add(n.typ)
 					sc.sym[c.ident] = &symbol{index: index, kind: varSym, typ: n.typ}
@@ -1878,8 +1886,15 @@ func compDefineX(sc *scope, n *node) error {
 		if err != nil {
 			return err
 		}
+		for funtype.cat == valueT && funtype.val != nil {
+			// Retrieve original interpreter type from a wrapped function.
+			// Struct fields of function types are always wrapped in valueT to ensure
+			// their possible use in runtime. In that case, the val field retains the
+			// original interpreter type, which is used now.
+			funtype = funtype.val
+		}
 		if funtype.cat == valueT {
-			// Handle functions imported from runtime
+			// Handle functions imported from runtime.
 			for i := 0; i < funtype.rtype.NumOut(); i++ {
 				types = append(types, &itype{cat: valueT, rtype: funtype.rtype.Out(i)})
 			}
@@ -1903,7 +1918,7 @@ func compDefineX(sc *scope, n *node) error {
 		if n.child[0].ident == "_" {
 			n.child[l].gen = typeAssertStatus
 		} else {
-			n.child[l].gen = typeAssert2
+			n.child[l].gen = typeAssertLong
 		}
 		types = append(types, n.child[l].child[1].typ, sc.getType("bool"))
 		n.gen = nop
@@ -2473,6 +2488,8 @@ func compositeGenerator(n *node, typ *itype, rtyp reflect.Type) (gen bltnGenerat
 			gen = compositeBinMap
 		case reflect.Ptr:
 			gen = compositeGenerator(n, typ, n.typ.val.rtype)
+		case reflect.Slice:
+			gen = compositeBinSlice
 		default:
 			log.Panic(n.cfgErrorf("compositeGenerator not implemented for type kind: %s", k))
 		}

interp/gta.go

@@ -115,6 +115,7 @@ func (interp *Interpreter) gta(root *node, rpath, importPath string) ([]*node, e
 					sc.sym[c.ident] = &symbol{index: sc.add(n.typ), kind: varSym, global: true, typ: n.typ, node: n}
 					continue
 				}
+				c.level = globalFrame
 
 				// redeclaration error
 				if sym.typ.node != nil && sym.typ.node.anc != nil {

interp/interp.go

@@ -65,7 +65,8 @@ type frame struct {
 	// Located at start of struct to ensure proper aligment.
 	id uint64
 
-	anc  *frame          // ancestor frame (global space)
+	root *frame          // global space
+	anc  *frame          // ancestor frame (caller space)
 	data []reflect.Value // values
 
 	mutex     sync.RWMutex
@@ -80,8 +81,11 @@ func newFrame(anc *frame, len int, id uint64) *frame {
 		data: make([]reflect.Value, len),
 		id:   id,
 	}
-	if anc != nil {
+	if anc == nil {
+		f.root = f
+	} else {
 		f.done = anc.done
+		f.root = anc.root
 	}
 	return f
 }
@@ -93,6 +97,7 @@ func (f *frame) clone() *frame {
 	defer f.mutex.RUnlock()
 	return &frame{
 		anc:       f.anc,
+		root:      f.root,
 		data:      f.data,
 		deferred:  f.deferred,
 		recovered: f.recovered,
@@ -239,7 +244,7 @@ type Options struct {
 func New(options Options) *Interpreter {
 	i := Interpreter{
 		opt:      opt{context: build.Default},
-		frame:    &frame{data: []reflect.Value{}},
+		frame:    newFrame(nil, 0, 0),
 		fset:     token.NewFileSet(),
 		universe: initUniverse(),
 		scopes:   map[string]*scope{},

interp/run.go

@@ -69,7 +69,7 @@ var builtin = [...]bltnGenerator{
 	aStar:         deref,
 	aSub:          sub,
 	aSubAssign:    subAssign,
-	aTypeAssert:   typeAssert1,
+	aTypeAssert:   typeAssertShort,
 	aXor:          xor,
 	aXorAssign:    xorAssign,
 }
@@ -191,45 +191,6 @@ func runCfg(n *node, f *frame) {
 	}
 }
 
-func typeAssertStatus(n *node) {
-	c0, c1 := n.child[0], n.child[1]   // cO contains the input value, c1 the type to assert
-	value := genValue(c0)              // input value
-	value1 := genValue(n.anc.child[1]) // returned status
-	rtype := c1.typ.rtype              // type to assert
-	next := getExec(n.tnext)
-
-	switch {
-	case isInterfaceSrc(c1.typ):
-		typ := c1.typ
-		n.exec = func(f *frame) bltn {
-			v, ok := value(f).Interface().(valueInterface)
-			value1(f).SetBool(ok && v.node.typ.implements(typ))
-			return next
-		}
-	case isInterface(c1.typ):
-		n.exec = func(f *frame) bltn {
-			v := value(f)
-			ok := v.IsValid() && canAssertTypes(v.Elem().Type(), rtype)
-			value1(f).SetBool(ok)
-			return next
-		}
-	case c0.typ.cat == valueT || c0.typ.cat == errorT:
-		n.exec = func(f *frame) bltn {
-			v := value(f)
-			ok := v.IsValid() && canAssertTypes(v.Elem().Type(), rtype)
-			value1(f).SetBool(ok)
-			return next
-		}
-	default:
-		n.exec = func(f *frame) bltn {
-			v, ok := value(f).Interface().(valueInterface)
-			ok = ok && v.value.IsValid() && canAssertTypes(v.value.Type(), rtype)
-			value1(f).SetBool(ok)
-			return next
-		}
-	}
-}
-
 func stripReceiverFromArgs(signature string) (string, error) {
 	fields := receiverStripperRxp.FindStringSubmatch(signature)
 	if len(fields) < 5 {
@@ -241,25 +202,33 @@ func stripReceiverFromArgs(signature string) (string, error) {
 	return fmt.Sprintf("func(%s", fields[4]), nil
 }
 
-func typeAssert1(n *node) {
-	typeAssert(n, false)
+func typeAssertShort(n *node) {
+	typeAssert(n, true, false)
 }
 
-func typeAssert2(n *node) {
-	typeAssert(n, true)
+func typeAssertLong(n *node) {
+	typeAssert(n, true, true)
 }
 
-func typeAssert(n *node, withOk bool) {
+func typeAssertStatus(n *node) {
+	typeAssert(n, false, true)
+}
+
+func typeAssert(n *node, withResult, withOk bool) {
 	c0, c1 := n.child[0], n.child[1]
 	value := genValue(c0) // input value
 	var value0, value1 func(*frame) reflect.Value
 	setStatus := false
-	if withOk {
+	switch {
+	case withResult && withOk:
 		value0 = genValue(n.anc.child[0])       // returned result
 		value1 = genValue(n.anc.child[1])       // returned status
 		setStatus = n.anc.child[1].ident != "_" // do not assign status to "_"
-	} else {
+	case withResult && !withOk:
 		value0 = genValue(n) // returned result
+	case !withResult && withOk:
+		value1 = genValue(n.anc.child[1])       // returned status
+		setStatus = n.anc.child[1].ident != "_" // do not assign status to "_"
 	}
 
 	typ := c1.typ // type to assert or convert to
@@ -270,7 +239,8 @@ func typeAssert(n *node, withOk bool) {
 	switch {
 	case isInterfaceSrc(typ):
 		n.exec = func(f *frame) bltn {
-			v, ok := value(f).Interface().(valueInterface)
+			valf := value(f)
+			v, ok := valf.Interface().(valueInterface)
 			if setStatus {
 				defer func() {
 					value1(f).SetBool(ok)
@@ -283,7 +253,9 @@ func typeAssert(n *node, withOk bool) {
 				return next
 			}
 			if v.node.typ.id() == typID {
-				value0(f).Set(value(f))
+				if withResult {
+					value0(f).Set(valf)
+				}
 				return next
 			}
 			m0 := v.node.typ.methods()
@@ -329,7 +301,9 @@ func typeAssert(n *node, withOk bool) {
 				}
 			}
 
-			value0(f).Set(value(f))
+			if withResult {
+				value0(f).Set(valf)
+			}
 			return next
 		}
 	case isInterface(typ):
@@ -362,9 +336,9 @@ func typeAssert(n *node, withOk bool) {
 					}
 				}
 
-				// TODO(mpl): make this case compliant with reflect's Implements.
-				v = genInterfaceWrapper(val.node, rtype)(f)
-				value0(f).Set(v)
+				if withResult {
+					value0(f).Set(genInterfaceWrapper(val.node, rtype)(f))
+				}
 				ok = true
 				return next
 			}
@@ -392,7 +366,9 @@ func typeAssert(n *node, withOk bool) {
 				}
 				return next
 			}
+			if withResult {
 				value0(f).Set(v)
+			}
 			return next
 		}
 	case n.child[0].typ.cat == valueT || n.child[0].typ.cat == errorT:
@@ -410,6 +386,7 @@ func typeAssert(n *node, withOk bool) {
 				}
 				return next
 			}
+			v = valueInterfaceValue(v)
 			ok = canAssertTypes(v.Type(), rtype)
 			if !ok {
 				if !withOk {
@@ -418,7 +395,9 @@ func typeAssert(n *node, withOk bool) {
 				}
 				return next
 			}
+			if withResult {
 				value0(f).Set(v)
+			}
 			return next
 		}
 	default:
@@ -436,14 +415,23 @@ func typeAssert(n *node, withOk bool) {
 				}
 				return next
 			}
-			ok = canAssertTypes(v.value.Type(), rtype)
+
+			styp := v.value.Type()
+			// TODO(mpl): probably also maps and others. and might have to recurse too.
+			if styp.String() == "[]interp.valueInterface" {
+				styp = v.node.typ.rtype
+			}
+
+			ok = canAssertTypes(styp, rtype)
 			if !ok {
 				if !withOk {
 					panic(fmt.Sprintf("interface conversion: interface {} is %s, not %s", v.value.Type().String(), rtype.String()))
 				}
 				return next
 			}
+			if withResult {
 				value0(f).Set(v.value)
+			}
 			return next
 		}
 	}
@@ -907,11 +895,6 @@ func genFunctionWrapper(n *node) func(*frame) reflect.Value {
 				if v, ok := r.Interface().(*node); ok {
 					result[i] = genFunctionWrapper(v)(f)
 				}
-				if def.typ.ret[i].cat == interfaceT {
-					x := result[i].Interface().(valueInterface).value
-					result[i] = reflect.New(reflect.TypeOf((*interface{})(nil)).Elem()).Elem()
-					result[i].Set(x)
-				}
 			}
 			return result
 		})
@@ -1238,6 +1221,8 @@ func call(n *node) {
 
 func getFrame(f *frame, l int) *frame {
 	switch l {
+	case globalFrame:
+		return f.root
 	case 0:
 		return f
 	case 1:
@@ -1291,13 +1276,13 @@ func callBin(n *node) {
 			numOut := c.child[0].typ.rtype.NumOut()
 			for j := 0; j < numOut; j++ {
 				ind := c.findex + j
-				values = append(values, func(f *frame) reflect.Value { return f.data[ind] })
+				values = append(values, func(f *frame) reflect.Value { return valueInterfaceValue(f.data[ind]) })
 			}
 		case isRegularCall(c):
 			// Handle nested function calls: pass returned values as arguments
 			for j := range c.child[0].typ.ret {
 				ind := c.findex + j
-				values = append(values, func(f *frame) reflect.Value { return f.data[ind] })
+				values = append(values, func(f *frame) reflect.Value { return valueInterfaceValue(f.data[ind]) })
 			}
 		default:
 			if c.kind == basicLit || c.rval.IsValid() {
@@ -1391,9 +1376,13 @@ func callBin(n *node) {
 			for i := range rvalues {
 				c := n.anc.child[i]
 				if c.ident != "_" {
+					if c.typ.cat == interfaceT {
+						rvalues[i] = genValueInterfaceValue(c)
+					} else {
 						rvalues[i] = genValue(c)
 					}
 				}
+			}
 			n.exec = func(f *frame) bltn {
 				in := make([]reflect.Value, l)
 				for i, v := range values {
@@ -1734,6 +1723,13 @@ func getMethodByName(n *node) {
 
 	n.exec = func(f *frame) bltn {
 		val := value0(f).Interface().(valueInterface)
+		for {
+			v, ok := val.value.Interface().(valueInterface)
+			if !ok {
+				break
+			}
+			val = v
+		}
 		typ := val.node.typ
 		if typ.node == nil && typ.cat == valueT {
 			// happens with a var of empty interface type, that has value of concrete type
@@ -2166,7 +2162,11 @@ func arrayLit(n *node) {
 		for i, v := range values {
 			a.Index(index[i]).Set(v(f))
 		}
-		value(f).Set(a)
+		dest := value(f)
+		if _, ok := dest.Interface().(valueInterface); ok {
+			a = reflect.ValueOf(valueInterface{n, a})
+		}
+		dest.Set(a)
 		return next
 	}
 }
@@ -2233,6 +2233,51 @@ func compositeBinMap(n *node) {
 	}
 }
 
+func compositeBinSlice(n *node) {
+	value := valueGenerator(n, n.findex)
+	next := getExec(n.tnext)
+	child := n.child
+	if n.nleft == 1 {
+		child = n.child[1:]
+	}
+
+	values := make([]func(*frame) reflect.Value, len(child))
+	index := make([]int, len(child))
+	rtype := n.typ.rtype.Elem()
+	var max, prev int
+
+	for i, c := range child {
+		if c.kind == keyValueExpr {
+			convertLiteralValue(c.child[1], rtype)
+			values[i] = genValue(c.child[1])
+			index[i] = int(vInt(c.child[0].rval))
+		} else {
+			convertLiteralValue(c, rtype)
+			values[i] = genValue(c)
+			index[i] = prev
+		}
+		prev = index[i] + 1
+		if prev > max {
+			max = prev
+		}
+	}
+
+	typ := n.typ.frameType()
+	n.exec = func(f *frame) bltn {
+		var a reflect.Value
+		if n.typ.sizedef {
+			a, _ = n.typ.zero()
+		} else {
+			a = reflect.MakeSlice(typ, max, max)
+		}
+		for i, v := range values {
+			a.Index(index[i]).Set(v(f))
+		}
+		value(f).Set(a)
+		return next
+	}
+}
+
 // doCompositeBinStruct creates and populates a struct object from a binary type.
 func doCompositeBinStruct(n *node, hasType bool) {
 	next := getExec(n.tnext)

interp/scope.go

@@ -130,6 +130,9 @@ func (s *scope) lookup(ident string) (*symbol, int, bool) {
 	level := s.level
 	for {
 		if sym, ok := s.sym[ident]; ok {
+			if sym.global {
+				return sym, globalFrame, true
+			}
 			return sym, level - s.level, true
 		}
 		if s.anc == nil {

interp/value.go

@@ -5,8 +5,15 @@ import (
 	"reflect"
 )
 
+const (
+	notInFrame  = -1 // value of node.findex for literal values (not in frame)
+	globalFrame = -1 // value of node.level for global symbols
+)
+
 func valueGenerator(n *node, i int) func(*frame) reflect.Value {
 	switch n.level {
+	case globalFrame:
+		return func(f *frame) reflect.Value { return valueOf(f.root.data, i) }
 	case 0:
 		return func(f *frame) reflect.Value { return valueOf(f.data, i) }
 	case 1:
@@ -171,18 +178,16 @@ func genValue(n *node) func(*frame) reflect.Value {
 			return func(f *frame) reflect.Value { return v }
 		}
 		if n.sym != nil {
-			if n.sym.index < 0 {
+			i := n.sym.index
+			if i < 0 {
 				return genValue(n.sym.node)
 			}
-			i := n.sym.index
 			if n.sym.global {
-				return func(f *frame) reflect.Value {
-					return n.interp.frame.data[i]
-				}
+				return func(f *frame) reflect.Value { return f.root.data[i] }
 			}
 			return valueGenerator(n, i)
 		}
-		if n.findex < 0 {
+		if n.findex == notInFrame {
 			var v reflect.Value
 			if w, ok := n.val.(reflect.Value); ok {
 				v = w
@@ -297,6 +302,17 @@ func genValueOutput(n *node, t reflect.Type) func(*frame) reflect.Value {
 	return value
 }
 
+func valueInterfaceValue(v reflect.Value) reflect.Value {
+	for {
+		vv, ok := v.Interface().(valueInterface)
+		if !ok {
+			break
+		}
+		v = vv.value
+	}
+	return v
+}
+
 func genValueInterfaceValue(n *node) func(*frame) reflect.Value {
 	value := genValue(n)
 
@@ -307,7 +323,7 @@ func genValueInterfaceValue(n *node) func(*frame) reflect.Value {
 			v.Set(zeroInterfaceValue())
 			v = value(f)
 		}
-		return v.Interface().(valueInterface).value
+		return valueInterfaceValue(v)
 	}
 }