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  1. Functors

    Project Setup

    Check that this works using the opam exec -- dune exec funkt command. It shouldn't do anything (the empty file is valid OCaml syntax), but it shouldn't fail either. The stanza libraries str makes

    Module System

  2. Lists

    Maps and Iterators

    Notice that map2 and iter2 will fail if the lists are of unequal length: There is a variant iter2 for two lists too: In addition, we have an imperative analogue to map , called

    Introduction

  3. A Tour of OCaml

    Records

    Here, the pattern { age = x; _ } is typed with the most recently declared record type that has an age field of type int . The type int is inferred from the expression 13 <= x && x <= 19 . The

    First Steps

  4. OCaml on Windows

    Docker Images

    The ocaml/opam Docker Hub repository now contains regularly-updated Windows images. This includes images using msvc and mingw . If you are comfortable with Docker, this might be an easier w

    Resources

  5. Maps

    Introduction

    When we created the StringMap module, we fed the Map.Make functor the String module to define the type of the map's keys, which we can observe in the StringMap 's signature ( type key stri

    Data Structures

  6. Modules

    Module Inclusion

    It creates a module Extlib.List that has everything the standard List module has, plus a new uncons function. In order to override the default List module from another .ml file, we need

    Module System

  7. Basic Data Types and Pattern Matching

    Unit

    The function print_endline prints the string followed by a line ending on standard output. Return of the unit value means the output request has been queued by the operating system. Note : Replace

    Introduction

  8. Using the OCaml Playground

    Autocomplete

    Autocomplete in the OCaml Playground The playground also supports code completion. It helps users by suggesting and completing their input based on the context.

    Resources

  9. Using the OCaml Playground

    Bottom Line

    Congratulations! You have made it to the end. Hopefully, by now, you have a better idea how to use the OCaml Playground . Use this to practice the OCaml code and have fun. Happy Hacking!

    Resources

  10. Sets

    Adding an Element to a Set

    The function StringSet.add with type string -> StringSet.t -> StringSet.t takes both a string and a string set. It returns a new string set. Sets created with the Set.Make functor in OCaml are

    Data Structures

  11. Modules

    Stateful Modules

    Values returned by Random.bits will differ when you run this code. The first and third calls return the same results, showing that the internal state was reset. A module may have an internal

    Module System

  12. Lists

    List Searching

    Note that the documentation for filter and partition tells us that the order of the input is preserved in the output. Where this is not stated it the documentation, it cannot be assumed.

    Introduction

  13. Arrays

    The Standard Library Array Module

    OCaml provides several useful functions for working with arrays. Here are some of the most common ones:

    Data Structures

  14. Arrays

    Iterate on an Array

    Iterating on arrays can also be made using for loops. Here is the same example using a loop: Array.iter applies a function to each element of an array, one at a time. The given function must

    Data Structures

  15. Options

    Fold an Option

    Here is the same function, using Option.fold : The Option.fold function can be used to implement a fall-back logic without writing pattern matching. For instance, here is a function that turn

    Data Structures

  16. Using the OCaml Playground

    Caveat

    In contrast, when you separate these expressions with a ;; , like this , or when you bind them to names, like this , they are evaluated successfully, one after another. A little caveat here is

    Resources

  17. Error Handling

    Stack Traces

    And you will get a stack trace. Alternatively, you can call, from within the program, To get a stack trace when an unhandled exception makes your program crash, you need to compile the progr

    Guides

  18. Maps

    Removing Entries From a Map

    Note that the initial map lucky_numbers remains unchanged. Removing a key that isn't present in the map has no effect. To remove an entry from a map, use the remove function, which takes a ke

    Data Structures

  19. Arrays

    Introduction

    Storing and processing large amounts of data Implementing algorithms that require random access and modification of elements Working with matrices and other multi-dimensional data structures Arrays

    Data Structures

  20. Higher Order Functions

    Let-ops

    This has the advantage of making code a lot more readable, without changing the behavior we've come to expect from bind calls. Thankfully, OCaml lets us redefine a subset of operators called let-

    Introduction

  21. Options

    Bind an Option

    Observe that the types are the same, except for the codomain of the function parameter. Here, we display the type of Option.map , with parameters flipped and show a possible implementation of Op

    Data Structures

  22. Options

    Map Over an Option

    In the standard library, this is Option.map . Using pattern matching, it is possible to define functions, allowing to work with option values. Here is map of type ('a -> 'b) -> 'a option ->

    Data Structures

  23. Higher Order Functions

    Binding

    To do this with lists we can use the concat_map function, which looks like this: For example, if we have a list and we map over it with a function that returns a list, then we'll have a list of

    Introduction

  24. Options

    Introduction

    The option type is useful when the lack of data is better handled as the special value None rather than an exception. It is the type-safe version of returning error values. Since no wrapped data ha

    Data Structures

  25. Higher Order Functions

    Sorting

    Most OCaml modules include a compare function that can be pass in to sort : For lists, this operation returns a new sorted list: For arrays, this operation mutates the array in-place: Bot

    Introduction

  26. Functors

    Introduction

    Note : The files illustrating this tutorial are available as a Git repo . As suggested by the name, a functor is almost like a function. However, while the inputs and outputs of functions are val

    Module System

  27. Arrays

    Sorting an Array

    It sorts the provided array in place and in ascending order, according to the provided comparison function. Sorting performed by Array.sort modifies the content of the provided array, which is wh

    Data Structures

  28. A Tour of OCaml

    Exceptions

    The standard library provides several predefined exceptions. It is possible to define exceptions. Exceptions are caught using the try … with … construction: Note that exceptions do not appe

    First Steps

  29. Loops and Recursions

    Approach 1

    Get the length of the file and read it all at once using the really_input method. This is the simplest, but it might not work on channels that are not really files (e.g., reading keyboard input)

    Introduction

  30. Maps

    Adding Entries to a Map

    Note that the initial map lucky_numbers remains unchanged. If the passed key is already associated with a value, the passed value replaces it. To add an entry to a map, use the add function t

    Data Structures

  31. OCaml Programming Guidelines

    How to Program

    Always put your handiwork back on the bench, then polish it and repolish it.

    Resources

  32. OCaml Programming Guidelines

    Credits

    Thanks to all those who have already participated in the critique of this page: Daniel de Rauglaudre, Luc Maranget, Jacques Garrigue, Damien Doligez, Xavier Leroy, Bruno Verlyck, Bruno Petazzoni,

    Resources

  33. Sets

    Checking if an Element is Contained in a Set

    To check if an element is contained in a set, use the StringSet.mem function.

    Data Structures

  34. Error Handling

    Printing

    Each printer should take care of the exceptions it knows about, returning Some <printed exception> , and return None otherwise (let the other printers do the job). OCaml knows how to print it

    Guides

  35. Sets

    Removing an Element from a Set

    The function StringSet.remove with type string -> StringSet.t -> StringSet.t takes both a string and a string set. It returns a new string set without the given string.

    Data Structures

  36. Lists

    List Scanning

    So you can see how the standard library has evolved into its present state: pieces of frequently-used code are turned into useful general functions. This is rather clumsy, though. The standard l

    Introduction

  37. Modules

    Conclusion

    Functors, which act like functions from modules to modules Libraries, which are compiled modules bundled together Packages, which are installation and distribution units Going further, here are the o

    Module System

  38. Labelled and Optional Arguments

    Conclusion

    Functions can have named or optional parameters. Refer to the reference manual for more examples and details on labels.

    Introduction

  39. Sets

    Introduction

    type elt = string for the elements, and type t = Set.Make(String).t for the sets. This module also defines two types: After naming the newly-created module StringSet , OCaml's toplevel displays t

    Data Structures

  40. File Manipulation

    Reading

    Standard in_channel : stdin Commonly used functions: open_in , open_in_bin , close_in , close_in_noerr Open the file to obtain an in_channel Read characters from the channel. Reading consum

    Tutorials

  41. A Tour of OCaml

    Lists

    Note that the x :: v pattern in the second matching expression is used to destructure the list into its head x and tail v , where head is the first element of the list and tail is the rest o

    First Steps

  42. Higher Order Functions

    Mapping

    This is called mapping . For example, if we have a list of users, maybe we want to get a list of usernames. Or if we have an optional password, we may want to encrypt it only if it is set. In cont

    Introduction

  43. File Manipulation

    Writing

    Standard out_channel s: stdout , stderr Commonly used functions: open_out , open_out_bin , flush , close_out , close_out_noerr Open the file to obtain an out_channel Write to the channel

    Tutorials

  44. Profiling

    Arrays

    So arrays of floats are unboxed, as expected. (Each float in the array is 8 bytes long.) The assembler syntax is rather complex, but the bracketed expression -4(%ecx, %eax, 4) means "at the ad

    Guides

  45. A Tour of OCaml

    Conclusion

    In this tutorial, OCaml was used interactively. The next tutorial, Your First OCaml Program , shows you how to write OCaml files, how to compile them, and how to kickstart a project. <!-- 1. Values

    First Steps

  46. Sets

    Creating a Set

    There's another relevant function StringSet.of_seq: string Seq.t -> StringSet.t that creates a set from a sequence . Converting a list into a set using StringSet.of_list : A set with a sing

    Data Structures

  47. Preprocessors and PPXs

    Writing a PPX

    If you want to write your own PPX, the place to start is ppxlib's documentation .

    Advanced Topics

  48. Lists

    Sorting Lists

    The function Fun.flip reverses a binary function parameter order. The function List.sort , given a comparison function of type 'a -> 'a -> int (zero if equal, negative if first smaller, p

    Introduction

  49. Error Handling

    Runtime Crashes

    Although OCaml is a very safe language, it is possible to trigger unrecoverable errors at runtime.

    Guides

  50. Maps

    Checking if a Key is Contained in a Map

    To check if a key is a member of a map, use the mem function:

    Data Structures
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