From d0cb268e9dfbc2f9afc7b30d1ac1e19f66b775ef Mon Sep 17 00:00:00 2001
From: Andy Xu <xzdandy@gmail.com>
Date: Thu, 21 Sep 2023 21:36:40 -0700
Subject: [PATCH] Add support for function calls without input arguments:
 `FUNC()` (#1185)

- [x] Implementation
- [x] Testcases
---
 evadb/functions/function_bootstrap_queries.py | 10 ++++++-
 evadb/parser/evadb.lark                       |  2 +-
 evadb/parser/lark_visitor/_functions.py       |  2 +-
 .../short/test_select_executor.py             |  8 +++++
 test/util.py                                  | 29 ++++++++++++++++++-
 5 files changed, 47 insertions(+), 4 deletions(-)

diff --git a/evadb/functions/function_bootstrap_queries.py b/evadb/functions/function_bootstrap_queries.py
index cd75e9a65..e51e75638 100644
--- a/evadb/functions/function_bootstrap_queries.py
+++ b/evadb/functions/function_bootstrap_queries.py
@@ -49,6 +49,13 @@
     EvaDB_INSTALLATION_DIR
 )
 
+DummyNoInputFunction_function_query = """CREATE FUNCTION
+                  IF NOT EXISTS DummyNoInputFunction
+                  IMPL '{}/../test/util.py';
+        """.format(
+    EvaDB_INSTALLATION_DIR
+)
+
 fuzzy_function_query = """CREATE FUNCTION IF NOT EXISTS FuzzDistance
                     INPUT (Input_Array1 NDARRAY ANYTYPE, Input_Array2 NDARRAY ANYTYPE)
                     OUTPUT (distance FLOAT(32, 7))
@@ -197,7 +204,7 @@ def init_builtin_functions(db: EvaDBDatabase, mode: str = "debug") -> None:
     In 'release' mode, only release functions are loaded. In addition, in 'debug' mode,
     the function loads a smaller model to accelerate the test suite time.
 
-    Args:
+    Args:G
         mode (str, optional): The mode for loading functions, either 'debug' or 'release'.
         Defaults to 'debug'.
 
@@ -242,6 +249,7 @@ def init_builtin_functions(db: EvaDBDatabase, mode: str = "debug") -> None:
                 DummyObjectDetector_function_query,
                 DummyMultiObjectDetector_function_query,
                 DummyFeatureExtractor_function_query,
+                DummyNoInputFunction_function_query,
             ]
         )
 
diff --git a/evadb/parser/evadb.lark b/evadb/parser/evadb.lark
index 635dff94f..add5c026f 100644
--- a/evadb/parser/evadb.lark
+++ b/evadb/parser/evadb.lark
@@ -272,7 +272,7 @@ or_replace: OR REPLACE
 function_call: function         ->function_call           
     | aggregate_windowed_function   ->aggregate_function_call
 
-function: simple_id "(" (STAR | function_args) ")" dotted_id?
+function: simple_id "(" (STAR | function_args)? ")" dotted_id?
     
 aggregate_windowed_function: aggregate_function_name "(" function_arg ")"
                            | COUNT "(" (STAR | function_arg) ")"
diff --git a/evadb/parser/lark_visitor/_functions.py b/evadb/parser/lark_visitor/_functions.py
index 7baa4e66b..a3b5a868a 100644
--- a/evadb/parser/lark_visitor/_functions.py
+++ b/evadb/parser/lark_visitor/_functions.py
@@ -30,7 +30,7 @@ class Functions:
     def function(self, tree):
         function_name = None
         function_output = None
-        function_args = None
+        function_args = []
 
         for child in tree.children:
             if isinstance(child, Token):
diff --git a/test/integration_tests/short/test_select_executor.py b/test/integration_tests/short/test_select_executor.py
index 7dc1f757c..2e0f24fd8 100644
--- a/test/integration_tests/short/test_select_executor.py
+++ b/test/integration_tests/short/test_select_executor.py
@@ -434,3 +434,11 @@ def test_expression_tree_signature(self):
             signature,
             f"DummyMultiObjectDetector[{function_id}](MyVideo.data[{col_id}])",
         )
+
+    def test_function_with_no_input_arguments(self):
+        select_query = "SELECT DummyNoInputFunction();"
+        actual_batch = execute_query_fetch_all(self.evadb, select_query)
+        expected = Batch(
+            pd.DataFrame([{"dummynoinputfunction.label": "DummyNoInputFunction"}])
+        )
+        self.assertEqual(actual_batch, expected)
diff --git a/test/util.py b/test/util.py
index 732aabc15..d793d1431 100644
--- a/test/util.py
+++ b/test/util.py
@@ -33,7 +33,10 @@
 from evadb.configuration.constants import EvaDB_DATABASE_DIR, EvaDB_INSTALLATION_DIR
 from evadb.database import init_evadb_instance
 from evadb.expression.function_expression import FunctionExpression
-from evadb.functions.abstract.abstract_function import AbstractClassifierFunction
+from evadb.functions.abstract.abstract_function import (
+    AbstractClassifierFunction,
+    AbstractFunction,
+)
 from evadb.functions.decorators import decorators
 from evadb.functions.decorators.io_descriptors.data_types import (
     NumpyArray,
@@ -636,3 +639,27 @@ def classify_one(self, frames: np.ndarray):
         i = int(frames[0][0][0][0]) - 1
         label = self.labels[i % 2 + 1]
         return np.array([label])
+
+
+class DummyNoInputFunction(AbstractFunction):
+    @decorators.setup(cacheable=False, function_type="test", batchable=False)
+    def setup(self, *args, **kwargs):
+        pass
+
+    @property
+    def name(self) -> str:
+        return "DummyNoInputFunction"
+
+    @decorators.forward(
+        input_signatures=[],
+        output_signatures=[
+            PandasDataframe(
+                columns=["label"],
+                column_types=[NdArrayType.STR],
+                column_shapes=[(None,)],
+            )
+        ],
+    )
+    def forward(self, df: pd.DataFrame) -> pd.DataFrame:
+        ret = pd.DataFrame([{"label": "DummyNoInputFunction"}])
+        return ret