Add iterator support for file objects

src/runtime/file.cpp

@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+#include <cstdio>
 #include <cstring>
 #include <sstream>
 
@@ -161,6 +162,22 @@ Box* fileNew(BoxedClass* cls, Box* s, Box* m) {
     return open(s, m);
 }
 
+Box* fileIterNext(BoxedFile* s) {
+    return fileReadline1(s);
+}
+
+bool fileEof(BoxedFile* self) {
+    char ch = fgetc(self->f);
+    ungetc(ch, self->f);
+    return feof(self->f);
+}
+
+Box* fileIterHasNext(Box* s) {
+    assert(s->cls == file_cls);
+    BoxedFile* self = static_cast<BoxedFile*>(s);
+    return boxBool(!fileEof(self));
+}
+
 void setupFile() {
     file_cls->giveAttr("__name__", boxStrConstant("file"));
 
@@ -179,6 +196,10 @@ void setupFile() {
     file_cls->giveAttr("__enter__", new BoxedFunction(boxRTFunction((void*)fileEnter, typeFromClass(file_cls), 1)));
     file_cls->giveAttr("__exit__", new BoxedFunction(boxRTFunction((void*)fileExit, UNKNOWN, 4)));
 
+    file_cls->giveAttr("__iter__", file_cls->getattr("__enter__"));
+    file_cls->giveAttr("__hasnext__", new BoxedFunction(boxRTFunction((void*)fileIterHasNext, BOXED_BOOL, 1)));
+    file_cls->giveAttr("next", new BoxedFunction(boxRTFunction((void*)fileIterNext, STR, 1)));
+
     file_cls->giveAttr("softspace",
                        new BoxedMemberDescriptor(BoxedMemberDescriptor::BYTE, offsetof(BoxedFile, softspace)));
 

test/tests/file.py

@@ -28,3 +28,14 @@ f = open("/dev/null", 'r')
 print chop(str(f))
 f.close()
 print chop(str(f))
+
+# Support for iteration protocol.
+f = open('/dev/null')
+print iter(f) is f
+f.close()
+
+with open('../README.md') as f:
+    lines = list(f)
+    print lines[:5]
+    print lines[-5:]
+