Could not find stored procedure ISDATE

Question

Below is a function, from what I can see there are no errors but when I attempt to build it I get the error "Could not find Stored Procedure ISDATE"

On a second note, if anyway has any better solution to my issue rather than my logic here, please let me know.

The requirement is to have a base day and to append that day every month to denote a range. The issue comes if the base day is 29, 30 or 31 and Feb rolls around, you will receive an error from SQL saying it is not a valid date. This functions purpose is to take three date parts and try and make a valid date to return.

CREATE FUNCTION Configuration.CreateDate
(
    @Year INT,
    @Month INT,
    @Day INT
)
RETURNS DATE
AS
BEGIN
    DECLARE @ReturnDate DATE

    DECLARE @DateString varchar
    DECLARE @VaildDate INT = 0;

    WHILE @VaildDate = 0
        BEGIN 
            SET @DateString = CAST(@Year AS VARCHAR(4)) + '-' +CAST(@Month AS VARCHAR(4)) + '-' + CAST(@Day AS VARCHAR(4))

            IF ISDATE(@DateString) = 1
                SET @ReturnDate = CAST(@DateString AS DATE)
                SET @VaildDate = 1
            ELSE 
                SET @Day = @Day - 1
        END

    RETURN @ReturnDate

END
GO

Answer 1

IF ISDATE(@DateString) = 1

to be replaced with:

IF TRY_CAST(@DateString AS DATE) IS NOT NULL

Adjusted DDL of the entire function:

CREATE FUNCTION Configuration.CreateDate
(
    @Year INT,
    @Month INT,
    @Day INT
)
RETURNS DATE
AS
BEGIN
    DECLARE @ReturnDate DATE

    DECLARE @DateString varchar
    DECLARE @VaildDate INT = 0;

    WHILE @VaildDate = 0
        BEGIN 
            SET @DateString = CAST(@Year AS VARCHAR(4)) + '-' +CAST(@Month AS VARCHAR(4)) + '-' + CAST(@Day AS VARCHAR(4))

            IF TRY_CAST(@DateString AS DATE) IS NOT NULL
            BEGIN
                SET @ReturnDate = CAST(@DateString AS DATE)
                SET @VaildDate = 1
            END
            ELSE 
                SET @Day = @Day - 1
        END

    RETURN @ReturnDate

END

On a second note, if anyway has any better solution to my issue rather than my logic here, please let me know.

Consider to not use scalar functions for such purposes at all. If such logic really needs to be encapsulated into some function, choose an inline type of UDF, but not a scalar one.