--  ISLOGICAL, ISTEXT, ISNONTEXT and ISNUMBER check their argument 
--  for the required data type.
--
--  Different results with strings, numbers, booleans, BLANK
EVALUATE
VAR ValueToCheck = "SQLBI"
RETURN
{
    ( "ISLOGICAL (" & ValueToCheck & ")" , ISLOGICAL ( ValueToCheck )),
    ( "ISTEXT    (" & ValueToCheck & ")" , ISTEXT    ( ValueToCheck )),
    ( "ISNONTEXT (" & ValueToCheck & ")" , ISNONTEXT ( ValueToCheck )),
    ( "ISNUMBER  (" & ValueToCheck & ")" , ISNUMBER  ( ValueToCheck ))
}

--  When you pass a column as the argument, these functions
--  check the metadata of the column, not the specific 
--  content of the column in the current row
EVALUATE
VAR A = DATATABLE ( 
    "S", STRING, 
    "I", INTEGER,
    { 
        { "A", 1 },     -- "A" is a string
        { "B", 2 },     -- "B" is a string
        { "1", 1 }      -- "1" is considered a string, even though it contains a number
    }
)
VAR ValueToCheck = "SQLBI"
RETURN
{
     ( "ISTEXT(S)",   COUNTROWS ( FILTER ( A, ISTEXT   ( [S] ) ) ) ),
     ( "ISNUMBER(S)", COUNTROWS ( FILTER ( A, ISNUMBER ( [S] ) ) ) ),
     ( "ISTEXT(I)",   COUNTROWS ( FILTER ( A, ISTEXT   ( [I] ) ) ) ),
     ( "ISNUMBER(I)", COUNTROWS ( FILTER ( A, ISNUMBER ( [I] ) ) ) )
}