interp: support more type assertion cases

Fixes #955

interp/value.go

@@ -33,6 +33,30 @@ func valueOf(data []reflect.Value, i int) reflect.Value {
 	return reflect.Value{}
 }
 
+func genValueBinMethodOnInterface(n *node, defaultGen func(*frame) reflect.Value) func(*frame) reflect.Value {
+	if n == nil || n.child == nil || n.child[0] == nil ||
+		n.child[0].child == nil || n.child[0].child[0] == nil {
+		return defaultGen
+	}
+	if n.child[0].child[1] == nil || n.child[0].child[1].ident == "" {
+		return defaultGen
+	}
+	value0 := genValue(n.child[0].child[0])
+
+	return func(f *frame) reflect.Value {
+		val, ok := value0(f).Interface().(valueInterface)
+		if !ok {
+			return defaultGen(f)
+		}
+		typ := val.node.typ
+		if typ.node != nil || typ.cat != valueT {
+			return defaultGen(f)
+		}
+		meth, _ := typ.rtype.MethodByName(n.child[0].child[1].ident)
+		return meth.Func
+	}
+}
+
 func genValueRecvIndirect(n *node) func(*frame) reflect.Value {
 	v := genValueRecv(n)
 	return func(f *frame) reflect.Value { return v(f).Elem() }
@@ -55,6 +79,35 @@ func genValueRecv(n *node) func(*frame) reflect.Value {
 	}
 }
 
+func genValueBinRecv(n *node, recv *receiver) func(*frame) reflect.Value {
+	value := genValue(n)
+	binValue := genValue(recv.node)
+
+	v := func(f *frame) reflect.Value {
+		if def, ok := value(f).Interface().(*node); ok {
+			if def != nil && def.recv != nil && def.recv.val.IsValid() {
+				return def.recv.val
+			}
+		}
+
+		ival, _ := binValue(f).Interface().(valueInterface)
+		return ival.value
+	}
+
+	fi := recv.index
+	if len(fi) == 0 {
+		return v
+	}
+
+	return func(f *frame) reflect.Value {
+		r := v(f)
+		if r.Kind() == reflect.Ptr {
+			r = r.Elem()
+		}
+		return r.FieldByIndex(fi)
+	}
+}
+
 func genValueRecvInterfacePtr(n *node) func(*frame) reflect.Value {
 	v := genValue(n.recv.node)
 	fi := n.recv.index