Parse a function, returning a FunctionQuery
Syntax Examples....
// Numeric fields default to correct type
// (ie: IntFieldSource or FloatFieldSource)
// Others use explicit ord(...) to generate numeric field value
myfield
// OrdFieldSource
ord(myfield)
// ReverseOrdFieldSource
rord(myfield)
// LinearFloatFunction on numeric field value
linear(myfield,1,2)
// MaxFloatFunction of LinearFloatFunction on numeric field value or constant
max(linear(myfield,1,2),100)
// ReciprocalFloatFunction on numeric field value
recip(myfield,1,2,3)
// ReciprocalFloatFunction on ReverseOrdFieldSource
recip(rord(myfield),1,2,3)
// ReciprocalFloatFunction on LinearFloatFunction on ReverseOrdFieldSource
recip(linear(rord(myfield),1,2),3,4,5)