When I try to execute a stored procedure from a function, I get: "Only functions and extended stored procedures can be executed from within a function." That might depend on the version of SQL Server though.
You can, however, call a function from a stored procedure:
CREATE FUNCTION dbo.fn_DoubleValue
(
@val as int
)
RETURNS int
BEGIN
RETURN @val * 2
END
GO
CREATE PROCEDURE ValueTimes4
@val as int
AS
BEGIN
SELECT dbo.fn_DoubleValue(dbo.fn_DoubleValue(@val))
END
GO
EXEC ValueTimes4 4