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Enumeration over abstract collection of elements.
Enumerations are entirely functional and most of the operations do not actually require the allocation of data structures. Using enumerations to manipulate data is therefore efficient and simple. All data structures in ExtLib such as lists, arrays, etc. have support to convert from and to enumerations.
type'a t
Final functions
These functions consume the enumeration until it ends or an exception is raised by the first argument function.
fold2 is similar to fold but will fold over two enumerations at the same time until one of the two enumerations ends.
Indexed functions : these functions are similar to previous ones except that they call the function with one additional argument which is an index starting at 0 and incremented after each call to the function.
find f e returns the first element x of e such that f x returns true, consuming the enumeration up to and including the found element, or, raises Not_found if no such element exists in the enumeration, consuming the whole enumeration in the search.
Since find consumes a prefix of the enumeration, it can be used several times on the same enumeration to find the next element.
force e forces the application of all lazy functions and the enumeration of all elements, exhausting the enumeration.
An efficient intermediate data structure of enumerated elements is constructed and e will now enumerate over that data structure.
Lazy constructors
These functions are lazy which means that they will create a new modified enumeration without actually enumerating any element until they are asked to do so by the programmer (using one of the functions above).
When the resulting enumerations of these functions are consumed, the underlying enumerations they were created from are also consumed.
concat e returns an enumeration over all elements of all enumerations of e.
Constructors
In this section the word shall denotes a semantic requirement. The correct operation of the functions in this interface are conditional on the client meeting these requirements.
exceptionNo_more_elements
This exception shall be raised by the next function of make or from when no more elements can be enumerated, it shall not be raised by any function which is an argument to any other function specified in the interface.
val make :
next:(unit ->'a)->count:(unit -> int)->clone:(unit ->'at)->'at
This function creates a fully defined enumeration.
the next function shall return the next element of the enumeration or raise No_more_elements if the underlying data structure does not have any more elements to enumerate.
the count function shall return the actual number of remaining elements in the enumeration.
the clone function shall create a clone of the enumeration such as operations on the original enumeration will not affect the clone.
For some samples on how to correctly use make, you can have a look at implementation of ExtList.enum.
from next creates an enumeration from the next function. nextshall return the next element of the enumeration or raise No_more_elements when no more elements can be enumerated. Since the enumeration definition is incomplete, a call to clone or count will result in a call to force that will enumerate all elements in order to return a correct value.
count e returns the number of remaining elements in e without consuming the enumeration.
Depending of the underlying data structure that is implementing the enumeration functions, the count operation can be costly, and even sometimes can cause a call to force.
For users worried about the speed of count you can call the fast_count function that will give an hint about count implementation. Basically, if the enumeration has been created with make or init or if force has been called on it, then fast_count will return true.