functionDefn — Defines a function by associating a table with other information
functionDefn :  [name]
     (griddedTableRef | griddedTable | ungriddedTableRef | ungriddedTable)
| name (optional) - the name of this function definition | 
A functionDefn defines how function is represented in one of two possible ways: gridded (implies breakpoints), or ungridded (with explicit independent values for each point).
| function | 
| griddedTableRef | 
| griddedTable | 
| ungriddedTableRef | 
| ungriddedTable |