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  1. A Tour of OCaml

    Using the result Type

    So one may write: Another way to deal with errors in OCaml is by returning value of type result , which can represent either the correct result or an error. Here is how it is defined:

    First Steps

  2. Debugging

    Launching the Debugger

    Then the debugger answers with a banner and a prompt: We launch the debugger: At runtime, the program raises an uncaught exception Not_found . Suppose we want to find where and why this e

    Guides

  3. OCaml Programming Guidelines

    Width of the Page

    Justification : This width makes it possible to read the code on all displays and to print it in a legible font on a standard sheet. The page is 80 columns wide.

    Resources

  4. Command-line Arguments

    Sys.argv

    <!-- $MDX dir=examples --> Note that ocaml launched a subprocess that actually runs the program where argv is args.ml arg1 arg2 arg3 . You can also compile your program using ocamlopt -o ar

    Tutorials

  5. Fix Homebrew Errors on Apple M1

    Install CLT

    If they're not installed, let's install them now. You don't have to install all of XCode; you can install just the CLT by downloading them directly from Apple's Developer . Look for a non-beta versi

    Resources

  6. Profiling

    Further Reading

    <!--### Java dynamic dispatch **There are some serious mistakes in the last paragraph:** * Dynamic method dispatch itself is seldom a performance problem. In languages without multiple inheritance

    Guides

  7. Sequences

    Fibs with Seq.Cons

    <!-- Or with an int version ``` ocaml # ints_v2 1 |> Seq.take 10 |> List.of_seq;; - : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10] ``` --> This implementation successfully defines a producer of laz

    Data Structures

  8. Values and Functions

    Introduction

    We use UTop to understand these concepts by example. You are encouraged to modify the examples to gain a better understanding. In OCaml, functions are treated as values, so you can use functions as

    Introduction

  9. Maps

    Changing the Value Associated With a Key

    You should experiment with different update functions; several behaviors are possible. To change a key's associated value, use the update function. It takes a key, a map, and an update functio

    Data Structures

  10. OCaml Programming Guidelines

    Iterators

    In case of express need, be sure to add an explanatory comment. In my opinion, it's absolutely necessary! <!-- $MDX skip --> even though you get: <!-- $MDX skip --> On the other hand, avoid w

    Resources

  11. OCaml Programming Guidelines

    How to Compile

    The make utility is indispensable for managing the compilation and recompilation of programs. Sample make files can be found on The Hump . You can also consult the Makefiles for the OCam

    Resources

  12. Memory Representation of Values

    Conclusion

    Understanding the Garbage Collector Calling C Libraries Other recommended tutorials: We covered the precise mapping from OCaml types to their internal runtime representation in memory, which shou

    Runtime & Compiler

  13. Profiling

    Tail Recursion

    So that's pretty conclusive. Calling Tail__loop_56 will first print the string, and then jump back to the top, then print the string, and jump back, and so on forever. It's a simple loop, not

    Guides

  14. Values and Functions

    Pattern Matching on User-Defined Types

    This also works with user-defined types.

    Introduction

  15. Values and Functions

    Closures

    Inside the max_42 function, the environment contains an additional binding between the first parameter of max and the value 42. Partially applying arguments to a function also creates a new clo

    Introduction

  16. Basic Data Types and Pattern Matching

    Characters

    The module Uchar provides support for Unicode characters. Operations on char values are provided by the Stdlib and the Char modules. Values of type char correspond to the 256 symbols of

    Introduction

  17. Sequences

    Consumer Example: Seq.iter

    In print_seq , Seq.iter takes the function print_int and applies it to each element as they are generated. If List.iter was used, the whole integer list would be needed before displaying the

    Data Structures

  18. Error Handling

    Language Bugs

    Here is an example of such a bug: <https://github.com/ocaml/ocaml/issues/7241> Make sure the crash affects both compilers: bytecode and native Write a self-contained and minimal proof-of-concept co

    Guides

  19. Objects

    A Note About self

    The reference to self names the object, allowing you to call methods in the same class or pass the object to functions outside the class. In other words, it's exactly the same as this in C++

    Advanced Topics

  20. Arrays

    Folding an Array

    These functions derive a single value from the whole array. For example, they can be used to find the maximum element of an array: fold_right f a init computes f a.(0) (f a.(1) ( ... (f a.(n-1)

    Data Structures

  21. Maps

    Maps With Custom Key Types

    Note that our module has a type t and also a compare function. Now we can call the Map.Make functor to get a map for non-negative numbers: We'll start by defining a module for strings th

    Data Structures

  22. Sequences

    Producer Example: Seq.unfold

    This application of Seq.unfold has type unit -> int Seq.node , making it a function, a deferred producer. Each time this function is called, a new element is produced.

    Data Structures

  23. A Tour of OCaml

    Functions

    Some functions, such as String.ends_with have labelled parameters. Labels are useful when a function has several parameters of the same type; naming arguments allows to guess their purpose. Above,

    First Steps

  24. Sequences

    Fibs with Seq.cons

    This produces a never-ending recursion that leads to a stack overflow. <!-- Or with an int version: ```ocaml # let rec ints_v1 n = Seq.cons n (n + 1);; val fibs : int -> int -> int Seq.t = <fun> #

    Data Structures

  25. OCaml Programming Guidelines

    Naming Complex Arguments

    <!-- $MDX skip --> write <!-- $MDX skip --> In place of

    Resources

  26. Modules

    Submodule Implementation

    dune Definitions from a submodule are accessed by chaining module names, here Florence.Hello.print . Here is the updated dune file, with an additional executable: glasgow.ml florence.ml

    Module System

  27. Loops and Recursions

    Recursion

    In the first example, we'll read the whole file into memory (into a long string). There are essentially three possible approaches to this: Writing recursive functions requires a change in mindse

    Introduction

  28. Maps

    Finding Entries in a Map

    Note that find_first_opt and find_last_opt return the key-value pair, not just the value. The functions find_first and find_last behave similarly, except they throw exceptions instead of

    Data Structures

  29. Options

    The Standard Library Option Module

    Most of the functions in this section, as well as other useful ones, are provided by the OCaml standard library in the Stdlib.Option module.

    Data Structures

  30. Error Handling

    Exceptions

    Here, we add a variant Foo to the type exn and create a function that will raise this exception. Now, how do we handle exceptions? The construct is try ... with ... : Exceptions belong to

    Guides

  31. Basic Data Types and Pattern Matching

    Results

    Operations on results are provided by the Result module. Results are discussed in the Error Handling guide. The result type can be used to express that a function's outcome can be either succ

    Introduction

  32. File Manipulation

    Gotchas

    Don't forget to flush your out_channel s if you want to actually write something. This is particularly important if you are writing to non-files such as the standard output ( stdout ) or a socke

    Tutorials

  33. OCaml on Windows

    Vim and Emacs

    If you use Vim , the default Cygwin Vim will not work with Merlin. You will need install Vim separately. In addition to the usual instructions printed when installing Merlin, you may need to se

    Resources

  34. Mutability and Imperative Control Flow

    Arrays

    For a more detailed discussion on arrays, see the Arrays tutorial. the array location to update (when on the left-hand side of <- ), or the cell's content (when on the right-hand side of <- ). T

    Introduction

  35. File Manipulation

    Buffered Channels

    channels that write to a file: type out_channel channels that read from a file: type in_channel The normal way of opening a file in OCaml returns a channel . There are two kinds of channels:

    Tutorials

  36. Sequences

    Consumers vs Producers

    A function with a sequence parameter consumes it; it's a sequence consumer. A function with a sequence result produces it; it's a sequence producer. In both cases, consumption and production occurs o

    Data Structures

  37. Arrays

    Modifying Array Elements

    Note that this operation returns unit , not the modified array. even_numbers is modified in place as a side effect. To modify an element in an array, we simply assign a new value to it using th

    Data Structures

  38. Debugging

    Setting Break Points

    Now we can guess why List.assoc will fail to find "INRIA" in the list... Then, we can step and find what happens just before ( <|b|> ) List.assoc is about to be called in find_address : L

    Guides

  39. Configuring Your Editor

    Windows Users

    If you used the DkML distribution, you will need to: 1. Go to File > Preferences > Settings view (or press Ctrl , ) 2. Select User > Extensions > OCaml Platform 3. Uncheck OCaml: U

    Tooling

  40. Your First OCaml Program

    Conclusion

    <!-- TODO: link Project Quickstart If you're already familiar with lists, maps, and folds, and need to be productive as fast as possible, dive into the “Project Quickstart” guide. --> This tuto

    First Steps

  41. Modules

    Submodule With Signatures

    The first version made Florence.Hello.message public. In this version it can't be accessed from glasgow.ml . To define a submodule's interface, we can provide a module signature . This is do

    Module System

  42. Options

    Peel-Off Doubly Wrapped Options

    In the standard library, this is Option.join . Here is join of type 'a option option -> 'a option . It peels off one layer from a doubly wrapped option:

    Data Structures

  43. Arrays

    Accessing Array Elements

    You can access individual elements of an array using the .(index) syntax, with the index of the element you want to access. The index of the first element is 0, and the index of the last element

    Data Structures

  44. Basic Data Types and Pattern Matching

    Options

    Operations on options are provided by the Option module. Options are discussed in the Error Handling guide. Here is an example of pattern matching on an option value: The option type is a

    Introduction

  45. Values and Functions

    The Pipe Operator

    This is just like a Unix shell pipe. The pipe operator ( |> ) also avoids parentheses but in reversed order: function on right, argument on left.

    Introduction

  46. OCaml Programming Guidelines

    Delimiters

    A space should always follow a delimiter symbol, and spaces should surround operator symbols. It has been a great step forward in typography to separate words by spaces in order to make written t

    Resources

  47. A Tour of OCaml

    Anonymous Functions

    We can write anonymous functions and immediately apply them to a value: Anonymous functions do not have a name, and they are defined with the fun keyword:

    First Steps

  48. Basic Data Types and Pattern Matching

    Type Aliases

    This is mostly useful as a means of documentation or to shorten long type expressions. Just like values, any type can be given a name.

    Introduction

  49. Installing OCaml

    Join the Community

    Make sure you join the OCaml community . You'll find many community members on Discuss or Discord . These are great places to ask for help if you have any issues.

    First Steps

  50. Operators

    Unary Operators

    This allows users to write more compact code. However, be careful not to write excessively terse code, as it is harder to maintain. Understanding operators must be obvious to most readers, otherwise

    Advanced Topics
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