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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 -
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 -
Operators
Allowed Operators
OCaml has a subtle syntax; not everything is allowed as an operator symbol. An operator symbol is an identifier with a special syntax, so it must have the following structure:
Advanced Topics -
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 -
OCaml-CI
What is OCaml-CI?
OCaml-CI is a continuous integration service specifically designed for OCaml projects hosted on GitHub (and GitLab). It's built on the OCurrent pipeline framework and is hosted at ocaml.ci.dev .
Additional Tooling -
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 -
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 -
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 -
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 -
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 -
OCaml-CI
Key Features
Automatic multi-version testing : Tests against multiple OCaml compiler versions Multi-platform support : Tests on different operating systems Smart caching : Docker layer caching makes rebuilds fast
Additional Tooling -
Preprocessors and PPXs
Writing a PPX
If you want to write your own PPX, the place to start is ppxlib's documentation .
Advanced Topics -
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 -
Options
Conclusion
The option type in OCaml provides a powerful and type-safe way to represent values that may be absent, avoiding the pitfalls of exceptions. By leveraging functions such as map , join , get , va
Data Structures -
Operators
Prefix Operator
First character, either: ? ~ ! Following characters, at least one if the first character is ? or ~ , optional otherwise: $ & * + - / = > @ ^ | % <
Advanced Topics -
Error Handling
Runtime Crashes
Although OCaml is a very safe language, it is possible to trigger unrecoverable errors at runtime.
Guides -
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 -
Profiling
Summary
Write your program as simply as possible. If it takes too long to run, profile it to find out where it's spending its time and concentrate optimisations on just those areas. Check for unintention
Guides -
Functors
heap.ml
<!-- TODO: Create this section When several implementations of the same interface are needed at runtime, functors allow sharing of their common parts. ## Multiple Implementation of the Same Signat
Module System -
File Manipulation
Seeking
Whenever you write or read something to or from a channel, the current position changes to the next character after what you just wrote or read. Occasionally, you may want to skip to a particular
Tutorials -
Configuring Your Editor
Emacs
A major mode, which, among other things, supports syntax highlighting and the structuring of indentation levels A minor mode, which will interact with a language server (such as ocaml-lsp-server ).
Tooling -
Sets
Subtracting a Set from Another
With the function StringSet.diff , we can remove the elements of the second set from the first set.
Data Structures -
Modules
Introduction
Note : The files that illustrate this tutorial are available as a Git repo . Modules are collections of definitions grouped together. This is the basic means to organise OCaml software. Separate co
Module System -
Objects
Objects Without Class
Here we examine how to use objects pretty much like records, without necessarily using classes.
Advanced Topics -
Profiling
Floats
string_of_float isn't polymorphic, but suppose we have a polymorphic function foo : 'a -> unit taking one polymorphic argument. If we call foo with %eax containing 7, then this is equivalen
Guides -
Comparison of Standard Containers
Stack
Adding an element: O(1) Taking an element: O(1) Length: O(1) OCaml stacks are mutable last-in-first-out (LIFO) data structures. They are just like lists except they are mutable, i.e., adding an
Resources -
OCaml-CI
Step 4: Add a Status Badge (Optional)
Add this to your README:
Additional Tooling -
OCaml-CI
Testing Locally
This runs a local web interface at http://localhost:8080 showing how your project would be built. You can test how OCaml-CI would build your project locally:
Additional Tooling -
Libraries With Dune
Conclusion
The OCaml module system allows organising a project in many ways. Dune provides several means to arrange modules into libraries.
Module System -
Basic Data Types and Pattern Matching
Variants
Variants are also called tagged unions . They relate to the concept of disjoint union .
Introduction -
Lists
Folds
Here are some more redefinitions of familiar functions in terms of fold_left or fold_right . Can you work out how they operate? Unfortunately, the order of evaluation here is such that larg
Introduction -
Functors
Conclusion
Functor application essentially works the same way as function application: passing parameters and getting results. The difference is that we are passing modules instead of values. Beyond comfort, it
Module System -
OCaml-CI
The OCaml-CI CLI
The CLI allows you to interact with OCaml-CI programmatically — checking build status, viewing logs, cancelling or rebuilding jobs.
Additional Tooling -
Maps
Creating a Map
Example 2 : By Adding an Element Example 1 : By Annotation When you create your new map with an annotation By adding an element to the map: The type of the values can be specified in two ways: T
Data Structures -
Error Handling
Documentation
<!-- $MDX skip --> Functions that can raise exceptions should be documented like this:
Guides -
Maps
Merging Maps
pick_fst picks the result's value from the first map pick_snd picks the result's value from the second map drop drops both entries in the result map Here are examples of duplicate key resolut
Data Structures -
Loops and Recursions
Approach 2
The imperative approach uses a while loop that is broken out of using an exception.
Introduction -
Using OCaml with GitHub Actions
Basic Usage
Create .github/workflows/ci.yml :
Additional Tooling -
Profiling
Speed
But you will need to know some assembler to get the most out of this section. Don't be afraid! I'll help you out by translating the assembler into a C-like pseudocode (after all C is just a porta
Guides -
OCaml-CI
Installation & Usage
Or install it as ocaml-ci . You can run it via dune:
Additional Tooling -
Sets
Intersection of Two Sets
With the function StringSet.inter , we can compute the intersection of two sets.
Data Structures -
Arrays
Map an Array
The Array.map function creates a new array by applying a given function to each element of an array. For example, we can get an array containing the square of each number in the even_numbers ar
Data Structures -
OCaml-CI
Requirements
You need a capability file ( ocaml-ci.cap ) which grants access to the API. This file must be provided to you by the OCaml-CI administrators.
Additional Tooling -
Arrays
Conclusion
In this tutorial, we covered the basics of arrays in OCaml, including how to create and manipulate them, as well as some of the most useful functions and use cases. Please refer to the standard libr
Data Structures -
OCaml on Windows
WSL2
After you have installed WSL2 and chosen one Linux distribution (we suggest Ubuntu LTS ), you can follow the Installing OCaml: Installation for Linux and macOS steps. If you only need to run O
Resources -
Comparison of Standard Containers
Queue
Adding an element: O(1) Taking an element: O(1) Length: O(1) OCaml queues are mutable first-in-first-out (FIFO) data structures.
Resources -
Sets
Filtering a Set
The function StringSet.filter of type (string -> bool) -> StringSet.t -> StringSet.t creates a new set by keeping the elements that satisfy a predicate from an existing set.
Data Structures -
Profiling
.data
.long writes a word (4 bytes) to the current segment. .byte writes a single byte. .ascii writes a string of bytes (NOT nul-terminated). .space writes the given number of zero bytes. Normall
Guides -
Maps
Filtering a Map
To filter a map, use the filter function. It takes a predicate to filter entries and a map. It returns a new map containing the entries satisfying the predicate.
Data Structures -
Preprocessors and PPXs
PPXs
PPxs are a different kind of preprocessor—one that does not run on the textual source code, but rather on the parsing result: the Abstract Syntax Tree (AST), which in the OCaml compiler is call
Advanced Topics