I'm not 100% sure I understand, but when I see "small functions of reusable code", the first thing that comes to mind are Modules. These are bits of OtterScript that you can from OtterScript using the call statement.
module Get-DomainMembership<$Param1, $OptionalParam2 = default, out $OutParam>
{
set $outParam = hello;
}
call Get-DomainMembership
(
Param1: some value,
Param2 => $SomeVariable
);
And then there are also Script Assets, which are PowerShell scripts that you call using the pscall operation from within OtterScript.
Is this helpful?