Support for calling functions without any arguments

[americast]

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• I have searched the EvaDB issues and found no similar feature requests.

Description

There might be a need to call a function without any arguments. Currently, calling SELECT <function>() FROM <table>; gives this error:

    raise UnexpectedToken(token, e.allowed, state=parser_state, token_history=[last_token], terminals_by_name=self.root_lexer.terminals_by_name)
lark.exceptions.UnexpectedToken: Unexpected token Token('RR_BRACKET', ')') at line 1, column 17.
Expected one of: 
        * MAX
        * AVG
        * DECIMAL_LITERAL
        * SUM
        * ONE_DECIMAL
        * MINUS
        * LR_SQ_BRACKET
        * LR_BRACKET
        * COUNT
        * BIT_NOT_OP
        * TRUE
        * FALSE
        * LOCAL_ID
        * STRING_LITERAL
        * TWO_DECIMAL
        * SEGMENT
        * STAR
        * REVERSE_QUOTE_ID
        * PLUS
        * ID
        * MIN
        * FIRST
        * REAL_LITERAL
        * ANYDIM
        * NOT
        * LAST
        * EXCLAMATION_SYMBOL
        * ZERO_DECIMAL
Previous tokens: [Token('LR_BRACKET', '(')]

while calling SELECT <function>(); results in

    raise UnexpectedToken(token, e.allowed, state=parser_state, token_history=[last_token], terminals_by_name=self.root_lexer.terminals_by_name)
lark.exceptions.UnexpectedToken: Unexpected token Token('RR_BRACKET', ')') at line 1, column 17.
Expected one of: 
        * ONE_DECIMAL
        * LR_SQ_BRACKET
        * COUNT
        * SEGMENT
        * STRING_LITERAL
        * MIN
        * STAR
        * TRUE
        * LR_BRACKET
        * NOT
        * FIRST
        * REAL_LITERAL
        * BIT_NOT_OP
        * LAST
        * ZERO_DECIMAL
        * PLUS
        * REVERSE_QUOTE_ID
        * FALSE
        * MINUS
        * AVG
        * ANYDIM
        * LOCAL_ID
        * SUM
        * DECIMAL_LITERAL
        * ID
        * MAX
        * TWO_DECIMAL
        * EXCLAMATION_SYMBOL
Previous tokens: [Token('LR_BRACKET', '(')]

Use case

We expect to call SELECT <function>(); without any error. It will help call functions that are specific to data when they are created.

Are you willing to submit a PR?

• Yes I'd like to help by submitting a PR!

[gaurav274]

@xzdandy This is fixed, right?

[gaurav274]

@americast @xzdandy Are we going to go with SELECT <function>(); or SELECT <function>() from table;?

[xzdandy]

This is not fixed. For now SELECT <function>(); is recommended. We need optimize SELECT <function>() from table; so if does not actually read the table (when the table is large it can take time). To systemically support it, it can be non trivial.

[xzdandy]

The problem can be reproduced using the following dummy function and queries:

Function defined in test/util.py:

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

Queries:

import evadb
cursor = evadb.connect().cursor()

df = cursor.query("""
    CREATE OR REPLACE FUNCTION DummyNoInputFunction
    IMPL 'test/util.py'
""").df()
print(df)

df = cursor.query("SELECT DummyNoInputFunction();").df()
print(df)

Looking into the fix now.