ocaml-containers/README.adoc

= OCaml-containers =
:toc: macro
:source-highlighter: pygments

A modular, clean and powerful extension of the OCaml standard library.

Containers is an extension of OCaml's standard library (under BSD license)
focused on data structures, combinators and iterators, without dependencies on
unix, str or num. Every module is independent and is prefixed with 'CC' in the
global namespace. Some modules extend the stdlib (e.g. CCList provides safe
map/fold_right/append, and additional functions on lists).
Alternatively, `open Containers` will bring enhanced versions of the standard
modules into scope.

image:https://ci.cedeela.fr/buildStatus/icon?job=containers[alt="Build Status", link="http://ci.cedeela.fr/job/containers/"]

toc::[]

== Quick Summary

Containers is:

- A usable, reasonably well-designed library that extends OCaml's standard
  library (in 'src/core/', packaged under `containers` in ocamlfind. Modules
  are totally independent and are prefixed with `CC` (for "containers-core"
  or "companion-cube" because I'm megalomaniac). This part should be
  usable and should work. For instance, `CCList` contains functions and
  lists including safe versions of `map` and `append`. It also
  provides a drop-in replacement to the standard library, in the module
  `Containers` (intended to be opened, replaces some stdlib modules
  with extended ones).
- Several small additional libraries that complement it:
  * `containers.data` with additional data structures that don't have an
    equivalent in the standard library;
  * `containers.iter` with list-like and tree-like iterators;
- Utilities around the `unix` library in `containers.unix` (mainly to spawn
  sub-processes easily and deal with resources safely)
- A lightweight S-expression printer and streaming parser in `containers.sexp`
- A library for threaded programming in `containers.thread`,
  including a blocking queue, semaphores, an extension of `Mutex`, and
  thread-pool based futures.

Some of the modules have been moved to their own repository (e.g. `sequence`,
`gen`, `qcheck`) and are on opam for great fun and profit.

== Change Log

See link:CHANGELOG.adoc[this file].

== Finding help

- http://lists.ocaml.org/listinfo/containers-users[Mailing List]
  the address is mailto:containers-users@lists.ocaml.org[]
- the https://github.com/c-cube/ocaml-containers/wiki[github wiki]
- on IRC, ask `companion_cube` on `#ocaml@freenode.net`
- image:https://badges.gitter.im/Join%20Chat.svg[alt="Gitter", link="https://gitter.im/c-cube/ocaml-containers?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge"]

== Use

You might start with the <<tutorial>> to get a picture of how to use the library.

You can either build and install the library (see <<build>>), or just copy
files to your own project. The last solution has the benefits that you
don't have additional dependencies nor build complications (and it may enable
more inlining). Since modules have a friendly license and are mostly
independent, both options are easy.

In a toplevel, using ocamlfind:

[source,OCaml]
----
# #use "topfind";;
# #require "containers";;
# CCList.flat_map;;
- : ('a -> 'b list) -> 'a list -> 'b list = <fun>
# open Containers;;  (* optional *)
# List.flat_map ;;
- : ('a -> 'b list) -> 'a list -> 'b list = <fun>
----

If you have comments, requests, or bugfixes, please share them! :-)

== License

This code is free, under the BSD license.

== Contents

See http://c-cube.github.io/ocaml-containers/[the documentation]
and <<tutorial,the tutorial below>> for a gentle introduction.

== Documentation

In general, see http://c-cube.github.io/ocaml-containers/ or
http://cedeela.fr/~simon/software/containers for the **API documentation**.

Some examples can be found link:doc/containers.adoc[there].

API documentation by version:

- http://c-cube.github.io/ocaml-containers/dev/[dev branch]
- http://c-cube.github.io/ocaml-containers/1.0/[1.0]
- http://c-cube.github.io/ocaml-containers/0.19/[0.19]
- http://c-cube.github.io/ocaml-containers/0.17/[0.17]

[[build]]
== Build

You will need OCaml `>=` 4.01.0.

=== Via opam

The prefered way to install is through http://opam.ocaml.org/[opam].

    $ opam install containers

=== From Sources

On the branch `master` you will need `oasis` to build the library. On the
branch `stable` it is not necessary.

    $ make

To build and run tests (requires `oUnit` and https://github.com/vincent-hugot/iTeML[qtest]):

    $ opam install oUnit qtest
    $ ./configure --enable-tests --enable-unix
    $ make test

To build the small benchmarking suite (requires https://github.com/chris00/ocaml-benchmark[benchmark]):

    $ opam install benchmark
    $ make bench
    $ ./benchs.native

== Contributing

PRs on github are welcome (patches by email too, if you prefer so).

A few guidelines:

- no dependencies between basic modules (even just for signatures);
- add `@since` tags for new functions;
- add tests if possible (using `qtest`).

Powered by image:http://oasis.forge.ocamlcore.org/oasis-badge.png[alt="OASIS", style="border: none;", link="http://oasis.forge.ocamlcore.org/"]

[[tutorial]]
== Tutorial

This tutorial contains a few examples to illustrate the features and
usage of containers. We assume containers is installed and that
the library is loaded, e.g. with:

[source,OCaml]
----
#require "containers";;
----

=== Basics

We will start with a few list helpers, then look at other parts of
the library, including printers, maps, etc.

[source,OCaml]
----

(* quick reminder of this awesome standard operator *)
# (|>) ;;
- : 'a -> ('a -> 'b) -> 'b = <fun>

# open CCList.Infix;;

# let l = 1 -- 100;;
val l : int list = [1; 2; .....]

# l
  |> CCList.filter_map
     (fun x-> if x mod 3=0 then Some (float x) else None)
  |> CCList.take 5 ;;
- : float list = [3.; 6.; 9.; 12.; 15.]

# let l2 = l |> CCList.take_while (fun x -> x<10) ;;
val l2 : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9]

(* an extension of Map.Make, compatible with Map.Make(CCInt) *)
# module IntMap = CCMap.Make(CCInt);;

(* conversions using the "sequence" type, fast iterators that are
   pervasively used in containers. Combinators can be found
   in the opam library "sequence". *)
# let map =
    l2
    |> List.map (fun x -> x, string_of_int x)
    |> CCList.to_seq
    |> IntMap.of_seq;;
val map : string CCIntMap.t = <abstr>

(* check the type *)
# CCList.to_seq ;;
- : 'a list -> 'a sequence = <fun>
# IntMap.of_seq ;;
- : (int * 'a) CCMap.sequence -> 'a IntMap.t = <fun>

(* we can print, too *)
# Format.printf "@[<2>map =@ @[<hov>%a@]@]@."
    (IntMap.print CCFormat.int CCFormat.string_quoted)
    map;;
map =
  [1 --> "1", 2 --> "2", 3 --> "3", 4 --> "4", 5 --> "5", 6 --> "6",
   7 --> "7", 8 --> "8", 9 --> "9"]
- : unit = ()

(* options are good *)
# IntMap.get 3 map |> CCOpt.map (fun s->s ^ s);;
- : string option = Some "33"

----

=== New types: `CCVector`, `CCHeap`, `CCResult`

Containers also contains (!) a few datatypes that are not from the standard
library but that are useful in a lot of situations:

CCVector::
  A resizable array, with a mutability parameter. A value of type
  `('a, CCVector.ro) CCVector.t` is an immutable vector of values of type `'a`,
  whereas a `('a, CCVector.rw) CCVector.t` is a mutable vector that
  can be modified. This way, vectors can be used in a quite functional
  way, using operations such as `map` or `flat_map`, or in a more
  imperative way.
CCHeap::
  A priority queue (currently, leftist heaps) functorized over
  a module `sig val t val leq : t -> t -> bool` that provides a type `t`
  and a partial order `leq` on `t`.
CCResult::
  An error type for making error handling more explicit (an error monad,
  really, if you're not afraid of the "M"-word).
  Subsumes and replaces the old `CCError`.
  It uses the new `result` type from the standard library (or from
  the retrocompatibility package on opam) and provides
  many combinators for dealing with `result`.

Now for a few examples:

[source,OCaml]
----

(* create a new empty vector. It is mutable, for otherwise it would
   not be very useful. *)
# CCVector.create;;
- : unit -> ('a, CCVector.rw) CCVector.t = <fun>

(* init, similar to Array.init, can be used to produce a
   vector that is mutable OR immutable (see the 'mut parameter?) *)
# CCVector.init ;;
- : int -> (int -> 'a) -> ('a, 'mut) CCVector.t = <fun>c

(* use the infix (--) operator for creating a range. Notice
   that v is a vector of integer but its mutability is not
   decided yet. *)
# let v = CCVector.(1 -- 10);;
val v : (int, '_a) CCVector.t = <abstr>

# Format.printf "v = @[%a@]@." (CCVector.print CCInt.print) v;;
v = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

(* now let's mutate v *)
# CCVector.push v 42;;
- : unit = ()

(* now v is a mutable vector *)
# v;;
- : (int, CCVector.rw) CCVector.t = <abstr>

(* functional combinators! *)
# let v2 = v
  |> CCVector.map (fun x-> x+1)
  |> CCVector.filter (fun x-> x mod 2=0)
  |> CCVector.rev ;;
val v2 : (int, '_a) CCVector.t = <abstr>

# Format.printf "v2 = @[%a@]@." (CCVector.print CCInt.print) v2;;
v2 = [10, 8, 6, 4, 2]

(* let's transfer to a heap *)
# module IntHeap = CCHeap.Make(struct type t = int let leq = (<=) end);;

# let h = v2 |> CCVector.to_seq |> IntHeap.of_seq ;;
val h : IntHeap.t = <abstr>

(* We can print the content of h
  (printing is not necessarily in order, though) *)
# Format.printf "h = [@[%a@]]@." (IntHeap.print CCInt.print) h;;
h = [2,4,6,8,10]

(* we can remove the first element, which also returns a new heap
   that does not contain it — CCHeap is a functional data structure *)
# IntHeap.take h;;
- : (IntHeap.t * int) option = Some (<abstr>, 2)

# let h', x = IntHeap.take_exn h ;;
val h' : IntHeap.t = <abstr>
val x : int = 2

(* see, 2 is removed *)
# IntHeap.to_list h' ;;
- : int list = [4; 6; 8; 10]

----

=== IO helpers

The core library contains a module called `CCIO` that provides useful
functions for reading and writing files. It provides functions that
make resource handling easy, following
the pattern `with_resource : resource -> (access -> 'a) -> 'a` where
the type `access` is a temporary handle to the resource (e.g.,
imagine `resource` is a file name and `access` a file descriptor).
Calling `with_resource r f` will access `r`, give the  result to `f`,
compute the result of `f` and, whether `f` succeeds or raises an
error, it will free the resource.

Consider for instance:

[source,OCaml]
----
# CCIO.with_out "/tmp/foobar"
    (fun out_channel ->
      CCIO.write_lines_l out_channel ["hello"; "world"]);;
- : unit = ()
----

This just opened the file '/tmp/foobar', creating it if it didn't exist,
and wrote two lines in it. We did not have to close the file descriptor
because `with_out` took care of it. By the way, the type signatures are:

[source,OCaml]
----
val with_out :
  ?mode:int -> ?flags:open_flag list ->
  string -> (out_channel -> 'a) -> 'a

val write_lines_l : out_channel -> string list -> unit
----

So we see the pattern for `with_out` (which opens a function in write
mode and gives its functional argument the corresponding file descriptor).

NOTE: you should never let the resource escape the
scope of the `with_resource` call, because it will not be valid outside.
OCaml's type system doesn't make it easy to forbid that so we rely
on convention here (it would be possible, but cumbersome, using
a record with an explicitely quantified function type).

Now we can read the file again:

[source,OCaml]
----
# let lines = CCIO.with_in "/tmp/foobar" CCIO.read_lines_l ;;
val lines : string list = ["hello"; "world"]
----

There are some other functions in `CCIO` that return _generators_
instead of lists. The type of generators in containers
is `type 'a gen = unit -> 'a option` (combinators can be
found in the opam library called "gen"). A generator is to be called
to obtain successive values, until it returns `None` (which means it
has been exhausted). In particular, python users might recognize
the function

[source,OCaml]
----
# CCIO.File.walk ;;
- : string -> walk_item gen = <fun>;;
----

where `type walk_item = [ `Dir | `File ] * string` is a path
paired with a flag distinguishing files from directories.


=== To go further: containers.data

There is also a sub-library called `containers.data`, with lots of
more specialized data-structures.
The documentation contains the API for all the modules
(see link:README.adoc[the readme]); they also provide
interface to `sequence` and, as the rest of containers, minimize
dependencies over other modules. To use `containers.data` you need to link it,
either in your build system or by `#require containers.data;;`

A quick example based on purely functional double-ended queues:

[source,OCaml]
----
# #require "containers.data";;
# #install_printer CCFQueue.print;;  (* better printing of queues! *)

# let q = CCFQueue.of_list [2;3;4] ;;
val q : int CCFQueue.t = queue {2; 3; 4}

# let q2 = q |> CCFQueue.cons 1 |> CCFQueue.cons 0 ;;
val q2 : int CCFQueue.t = queue {0; 1; 2; 3; 4}

(* remove first element *)
# CCFQueue.take_front q2;;
- : (int * int CCFQueue.t) option = Some (0, queue {1; 2; 3; 4})

(* q was not changed *)
# CCFQueue.take_front q;;
- : (int * int CCFQueue.t) option = Some (2, queue {3; 4})

(* take works on both ends of the queue *)
# CCFQueue.take_back_l 2 q2;;
- : int CCFQueue.t * int list = (queue {0; 1; 2}, [3; 4])

----

=== Common Type Definitions

Some structural types are used throughout the library:

gen:: `'a gen = unit -> 'a option` is an iterator type. Many combinators
  are defined in the opam library https://github.com/c-cube/gen[gen]
sequence:: `'a sequence = (unit -> 'a) -> unit` is also an iterator type.
  It is easier to define on data structures than `gen`, but it a bit less
  powerful.  The opam library https://github.com/c-cube/sequence[sequence]
  can be used to consume and produce values of this type.
error:: `'a or_error = ('a, string) result = Error of string | Ok of 'a`
  using the standard `result` type, supported in `CCResult`.
klist:: `'a klist = unit -> [`Nil | `Cons of 'a * 'a klist]` is a lazy list
  without memoization, used as a persistent iterator. The reference
  module is `CCKList` (in `containers.iter`).
printer:: `'a printer = Format.formatter -> 'a -> unit` is a pretty-printer
  to be used with the standard module `Format`. In particular, in many cases,
  `"foo: %a" Foo.print foo` will type-check.

=== Extended Documentation

See link:doc/containers.adoc[the extended documentation] for more examples.