Module List - Opa Documentation

About this module

This module defines lists (also known as "linked lists"), an immutable data structure meant
to contain finite or infinite sets of elements of the same type.

Where should I start?

To create a list containing elements 1, 2 and 3, the easiest is to write [1,2,3].
The empty list is []Once you have a list, typically, there may be a few things you wish to do with it:

Transforming lists

Do you have a list of numbers you wish to double? Try List.map. Or perhaps you only wish to keep
odd numbers? Look at List.filter. Or perhaps you wish to keep this in odd positions? Look atList.filteri.

Collecting list data

Do you wish to sum all the elements of a list? Try List.reduce. Or perhaps you only wish to find
the first even number? Try List.find. Or perhaps you wish to compute its length? Try List.length.

Sorting a list

To sort a list, use List.sort. This function can adapt to your sorting criteria.

Limitations of this module

What if I need more?

This module contains numerous other functions, including the all-powerful List.foldi, which will
let you apply arbitrary collections/transformations/loops based on the contents of a list.Lists are immutable, as are all base data structures in OPA -- this lets the compiler optimize numerous
operations, including concurrency and database access. If you need mutability, you should consider wrapping
your list in a Session.List provide linear access time, i.e. don't use them if you frequently need to add data at the end
or if you frequently need to access the nth element. For this purpose, you should rather use moduleArray.

Name	Summary
+>	As : adding an element at the head of a list.
add	An alias for Provided for compatibility with other collections.
add_uniq	A add in a list ordered by a function of comparison. Not tail rec, used for small list only in this ...
append	Concatenate two lists.Performance note: if you have a list you often need to extend at the end, rath...
assoc	Find the value associated to a key.
assoc_gen	As , but with control on the comparison function.Use this function rather than if you wish to use a...
check_length	Check that the list has the given lengthMore efficient that computing the length of the list and the...
collect	Transform a list by applying a function to each element and flattening the result.)] will return
compare
compose	returns: +++...+++where indicates application of function. You'll most likely not use this funct...
cons	Add an element at the start of a list returns the list whose first element is and in which the rest...
contains	As , but returns if the element can be found, not its index.
drop	Remove the first elements of a list.
empty	The empty listProvided for compatibility with other collections.
exists	Check whether at least one element of an index matches a given condition.
extract	Get and remove the element of a list.
extract_p	Extract an element from a list.
extract_pi	As but the function is informed of the position of the current element.
filter	Transform a list by removing some elements.
filter_map	Transform a list, removing some elements, changing others.This function lets you loop through a list...
filteri	As but the function is informed of the position of the current element.
find	As but returns the element itself, not its index.
find_map	Find the first element of a list verifying some condition and return it after treatment.This functio...
flatten	Flatten a list of list into a list.Performance note: this function is much faster than successive ca...
fold	Loop through a list, collecting data from the list., init)] will compute Example: the following expr...
fold2
fold_backwards	As but starting from the end.
fold_index	As .
fold_left	As
fold_map	Map a list while propagating an accumulator (l',accN) = fold_map(op, l, acc1) is equivalent to l' = ...
fold_right	As .
foldi	As but the function is informed of the position of the current element.
foldi_backwards	As but starting from the end.
foldl
foldl1
foldr
foldr1
for_all	Check whether all elements of an index match a given condition.
for_all2	Check whether all pair of corresponding elements of the pair of list match a given condition
get	Get the element of a list.Performance note: if you are looping through a list, you should rather us...
head
head_opt
index	Search for an element in a list.This function searches the first occurrence of an element in a list ...
index_p	Search for an element in a list.This function searches the first occurrence of any element matching ...
init	Create a list of elements from a function.
init_stable	A variant on . Slower but guarantees order of function calls.
insert_at	Insert an item in a list at a given position.
intersperse	Puts a constant separator between each element of the list
is_empty	Determine if a list is empty.
is_sorted	Check whether a list is sorted, by usual order.
is_sorted_by	Check whether a list is sorted, projecting elements before comparing them.
is_sorted_with	Check whether a list is sorted, using a custom order.
is_sorted_with_order	Check whether a list is sorted, using a custom order.
iter	Apply a function to all the elements of a list.By opposition to , , and their variants, this functi...
iterate	builds of length . (so the last element of the list has applications of )
iteri	As but informs the function of the current position in the list.)] will execute , , ...
length	Compute the length of a list.Performance note: if you only need to check whether a list is empty, yo...
list_to_string	Pretty-printing an arbitrary list using a value printer as: ]
make_order
map	Transform a list by applying a function to each element.)] will return
map2	Transform two lists by applying a function to each pair of elements at the same position.,)] will re...
map2_gen	Transforms two lists by applying a function to each pair of elements
map2_gen_aux
map_while_opt	Transform a list or give up.This function is a variant on which returns if any of the calls to the...
mapi	As , but the transformation function is informed of the current position in the list.
max
mem	Synonym to .
merge
merge_sort	Perform sorting on a list, using the merge sort algorithm.Performance note: This algorithm has compl...
merge_sort_with_order	Perform sorting on a list, using the merge sort algorithm.Performance note: This algorithm has compl...
merge_with_comparison
min
min_max
nil	An alias for the empty list
nth	As .
ordering
partition	Split a list in two.) ] returns , )]
partitioni	As but the function is informed of the position of the current element.
random_elt
remove	Remove the first occurrence of an element in a list.
remove_at	As but only returns the resulting list.
remove_p	As but only returns the resulting list.
remove_pi	As but only returns the resulting list.
rev	Revert a list.
rev_append	Revert a list and append it to another one.Performance note: This function is provided solely for pe...
rev_filter_map	As , but reverses the list.
rev_flatten	As , but reverses the list.
rev_init	As but in the reverse order.
rev_iter	Same as iter but in reverse order
rev_map	As , but reverses the list.
rev_mapi	As , but reverses the list.
sort	Sort a list by usual order.This function uses the order defined by function . The sort algorithm use...
sort_by	Sort a list by usual order, projecting elements before comparing them.This function first projects e...
sort_with	Sort a list with a custom order.This is a more powerful variant of .
sort_with_order	Sort a list with a custom order.This is a more powerful variant of .
split_at	Separate a list in two.
split_at_opt	Separate a list in two
split_between	Separate a list in two
split_middle	Separate a list in two halves.
tail
tail_opt
take	Keep the first elements of a list.
to_string	Pretty-printing a list of strings as: ]
to_string_using	Pretty-printing a list of strings as: ...
unique_list_of	Remove duplicates from a list.
unique_list_of_sorted	As but only works on sorted lists.
unsafe_get
unsafe_nth	As .
unzip	Separate a lists of pairs into two lists.
zip	Combine two lists into a list of pairs., )] will return