I've defined a function:

Public Class GeneralFunctions
Function StartsWith(ByVal sStart As String, ByVal sWord As String) As Boolean
Return Strings.Left(sWord, Len(sStart)).Equals(sStart)
End Function
End Class

Trying:
dim a = dt.Select("StartsWith(IssuerName,'abc')")

yields a runtime error: The expression contains undefined function call StartsWith()


Thinking is was a user defined issue I also tried:
dim a = dt.Select("Strings.Left(IssuerName, 1).Equals('B')"

and got: The expression contains undefined function call Strings.Left()

How are functions used in the filter expression of Datatable.Select?

thx