Ocaml format. formatter -> int -> unit val open_box : int -> unit val pp_close_box : Format. g. All components of this module can therefore be referred by their short name, without prefixing them by Stdlib. OCamlFormat is a tool to automatically format OCaml code. High-level and functional interface to the Format module of the OCaml standard library This module offers a high-level and functional interface to the Format module of the OCaml standard library. It is a pretty-printing facility, i. pos:int -> len:int -> Format. Sep 6, 2022 · Fun fact: there is a -strict-formats option that rejects many invalid formats instead of silently doing something. However, the box model is not that easy to grasp in practice (despite getting easier thanks to, e. it takes as input some code represented as a tree and formats this code into the most visually satisfying result, breaking and indenting lines of code where Format. The more general Module Format provides a complete set of printf like functions for pretty-printing using format string specifications. printf hello "Bob" Is there a more direct way of entering the hello format string literal than using ^^? May 5, 2024 · Hi folks, I wrote another monad Format tutorial. There is also a gentle guide to formatting text, something OCaml has fairly advanced support for because it turns out to be a pretty common requirement to print out the values of various things at runtime. These functions takes a callback which is called with the format string fully expanded. 2 and 5. In particular, it works by parsing source code using the OCaml compiler’s standard parser, deciding where to place comments in the parsetree, and printing the Feb 25, 2024 · More reading You can read more about OCaml's format strings functionality in the documentation for the Printf and Format modules. Does any of you know where I can find a decent tutorial for the OCaml Format module ? I cannot figure out how to use it, and the few things I have found are the documentation and the official tutorial, wh… Auto-formatter for OCaml code. The pretty-printing indication characters are introduced by a @ character, and their meanings are: The format module provides a general printing facility "a la" printf. Items marked with a * are likely to change your code. The format module provides a general printing facility "a la" printf. Additional dependencies OCamlFormat now requires: ocaml >= 4. 04. The name this idea is best known under is probably “printf”, which refers to the name of the C library function that implemented it. This package defines a RPC interface to OCamlFormat We would like to show you a description here but the site won’t allow us. We would like to show you a description here but the site won’t allow us. There have been numerous changes since the last release, so here is a comprehensive list of the new features and breaking changes to help the transition from OCamlFormat 0. Mar 29, 2019 · Release of OCamlFormat 0. Instead of giving a long style guide on how to format your OCaml code, we recommend that you use ocamlformat, which is an auto-formatter for OCaml code. com/pretty-printing-in-ocaml-a-format-primer Here’s some of layouts that are covered: [ [], ["one This module implements a pretty-printing facility to format values within 'pretty-printing boxes' and 'semantic tags' combined with a set of printf-like functions. Fmt depends only on the OCaml standard library. 26. Contribute to ocaml-ppx/ocamlformat development by creating an account on GitHub. . 10 This means both that it compiles and runs using this version, but also that it can format 4. Read more (in French) Format. To make it infer the right thing, you must use format_of_string (which is an identify function, but helps the type system): let fmt = format_of_string "Hello %s %d\n";; Printf. The pretty-printing indication characters are introduced by a @ character, and their meanings are: In OCaml there is an "overload" for string literals between strings and format thingies. It comes with opinionated default settings but is also fully customizable to suit your coding style. in_channel. Oct 28, 2024 · Also, using an ocaml-system compiler is more fragile than using an ocaml-base-compiler packaged by opam. It has a bunch of different built in profiles and many additional options to fine tune how the code should look like. Today, I looked more deeply into the Format module and I discover that it is more or less the Opinionated guidelines for writing OCaml codeOCaml Programming Guidelines This is a set of reasonable guidelines for writing OCaml programs that reflect the consensus among veteran OCaml programmers. ocaml -strict-formats # Printf. Projects like ocamlformat use it to implement very advanced code formatters. https://keleshev. It combines two distinct elements: pretty-print boxes semantic tags This tutorial aims to demystify much of this module and explain the range of things that you can do with it. Specific annotations may be added in the format strings to give pretty-printing commands to the pretty-printing engine. While I would encourage most people and new projects to use one of the default profiles, the many options are Pretty-printing library for OCaml. 06 (up from 4. No need for contributors to remember running OCamlformat, no need Auto-formatter for OCaml code OCamlFormat is a tool to automatically format OCaml code in a uniform style. I am generally familiar with the Printf module and use it happily. fprintf outchan format arg1 argN formats the arguments arg1 to argN according to the format string format, and outputs the resulting string on the channel outchan. In addition to editor plugins that use OCamlFormat for automatic code formatting, Dune also offers a command to run OCamlFormat to automatically format all files from your codebase: Still need help? The Format module of OCaml is an extremely powerful but unfortunately often poorly used module. File Manipulation This is a guide to basic file manipulation in OCaml using only the standard library. Jan 6, 2018 · kprintf is deprecated, you should use ksprintf instead. There are two kinds of channels: channels that write to a file: type out_channel Pretty-printing annotations are described below in the documentation of the function Format. Profiles include default, ocamlformat, janestreet. The format string is a character string which contains two types of objects: plain characters, which are simply copied to the output channel, and conversion specifications, each of which causes conversion and printing of The OCaml Standard library. 2. get_std_formatter and the generic version prefixed by pp_ that takes a formatter as its first argument. So I Sep 17, 2025 · Do we have an ocamlformat version that works both for 4. The pretty-printing indication characters are introduced by a @ character, and their meanings are: The format fmt is a character string which contains three types of objects: plain characters and conversion specifications as specified in the Printf module, and pretty-printing indications specific to the Format module. Auto-formatter for OCaml code ocamlformat is a code formatter for OCaml. formatter-> out: (string->int->int->unit)-> flush: (unit->unit)-> newline: (unit->unit)->spaces: (int->unit)->unit valpp_get_all_formatter_output_functions : The Format module of Caml Light and OCaml's standard libraries provides pretty-printing facilities to get a fancy display for printing routines. You can speed up code review by just focusing on the important parts OCaml library : Format sig typeformatter valpp_open_box :Format. It could include impact to module arguments, fun passed as a labelled argument, and indentation within parentheses. ocamlformat is a code formatter for OCaml. Jul 20, 2023 · We are happy to announce the release of OCamlFormat 0. Introduction Functional input with format strings The module Scanf provides formatted input functions or scanners. Format. You may also use the explicit box management and printing functions provided by this module. 3? (It seems answer is no) Without it I have difficulties with testing my code on different compilers. 1 octavius >= 1. Profiles: ocamlformat offers profiles we predefined formatting configurations. Official documentation for the modules of interest: the core library including the initially opened module Stdlib and Printf. e. 1) dune >= 1. formatter->int->unit valopen_box : int->unit valpp_close_box :Format. formatter->unit->unit valclose Oct 20, 2017 · OCamlFormat open-source released I’m pleased to announce the first public release of OCamlFormat. The format fmt is a character string which contains three types of objects: plain characters and conversion specifications as specified in the Printf module, and pretty-printing indications specific to the Format module. Contribute to ocaml-community/easy-format development by creating an account on GitHub. Module Format provides a complete set of printf like functions for pretty-printing using format string specifications. Feb 20, 2024 · I know there are projects like Fmt and ppx derivers that simplify the generation of pretty printers for OCaml objects, but in the general interest of knowing things, today I’m trying to discover the Stdlib way of doing such things. In particular, it provides the basic operations over the built-in types (numbers, booleans, byte sequences, strings, exceptions, references, lists, arrays, input-output channels Feb 28, 2023 · Continuing the discussion from Printf @@deriving sexp: Is there a variant of [%show: core type] that is a pp printer rather than generating a string? This module implements a pretty-printing facility to format values within 'pretty-printing boxes' and 'semantic tags' combined with a set of printf-like functions. OCaml source code can be formatted automatically with OCamlFormat, so you don't have to worry about formatting it by hand. Jun 6, 2025 · Topics tagged ocamlformatnext page →Topics tagged ocamlformat Opening an OCaml file should launch an ocaml-lsp server, and you can convince yourself that it's working by using, for example, the ocaml-eglot-type-enclosing command (or using the C-c C-t binding) on an expression of your choice: OCaml-eglot README provides a comprehensive overview of all the functions available in this mode! Vim Auto-formatter for OCaml code (RPC mode) OCamlFormat is a tool to automatically format OCaml code in a uniform style. The more general source of characters is named a formatted input channel (or scanning buffer) and has type Scanf. The pretty-printer splits lines at specified break hints, and indents lines according to the box structure. Here's how. 0, the auto-formatter for OCaml code. formatter -> int -> string -> unit val print_substring_as : pos:int -> len:int -> int -> string -> unit The format module provides a general printing facility "a la" printf. std_formatter outputs to stdout Format. 8. printf "%20a" (fun _ -> print_int) 42;; Error: invalid format "%20a": at character number 0, `padding' is incompatible with 'a' in sub-format "%20a" Benoît Vaugon and myself implemented this when we rewrote formatting support to use GADTs (Benoît OCaml Format pretty-printer combinators Fmt exposes combinators to devise Format pretty-printing functions. Similarly, semantic tags can be used to decouple text presentation from its contents. The The idea is to use a format specifier to —as the name suggest— specify how to format output. It follows the same basic design as refmt for Reason code, but for OCaml. I have currently two point: - Is it possible to have 4 spaces of indentation after a for/while statement? - Is it possible to force a if statement to wrap? Thank you and have a good day!! Format is a module in OCaml standard library that is used for writing pretty printers for code and data structures. This module implements a “pretty-printing engine” that is intended to break lines in a nice way (let's say “automatically when it is necessary”). The complete list of changes is here. Module Format provides a complete set of printf like functions for pretty-printing using format string specifications. The optional Fmt_tty library that allows to setup formatters for terminal color output depends on the Unix library. The format string is a character string which contains two types of objects: plain characters, which are simply copied to the output channel, and conversion specifications, each of which causes conversion and printing of Nov 12, 2022 · Hey, I just installed ocamlformat because I’m studying in class with ocaml and I’m trying to configure the formatter such as the code looks like how I was used to format it. This release contains changes that might affect your code and overall projects. 14. 1. Many other languages and libraries still use that name, including OCaml’s Printf module. Scanning. fprintf. Jul 1, 2022 · It is my pleasure to share with you the ocamlformat configurator as a web page. Ocamlformat is a great tool that really makes editing code a more pleasant experience. Installing different versions of ocamlformat seems to be not an option, because they format differently from version to version. The formatted input functions can read from any kind of input, including strings, files, or anything that can return characters. formatter -> unit -> unit val close_box The format string fmt is a character string which contains three types of objects: plain characters and conversion specifications as specified in the Printf module, and pretty-printing indications specific to the Format module. This module is automatically opened at the beginning of each compilation. Buffered Channels The normal way of opening a file in OCaml returns a channel. 0 uutf Jun 4, 2020 · Format string literals can be created and inferred correctly like: let hello = "" ^^ "Hello, %s!" let () = Printf. 9 We are pleased to announce the release of OCamlFormat (available on opam). Jun 29, 2017 · The Format module is quite powerful when one has to perform pretty-printing of various forms of data (programs for instance, or logical formulas…). This style is more basic but more verbose than the fprintf concise formats. In addition to the usual conversion facility provided by printf, you can write pretty-printing indications directly inside the format string (opening and closing boxes, indicating breaking hints, etc). I’m guessing you haven’t used the most-default-beginner-friendly way to install opam. For instance: Apr 3, 2020 · Support for OCaml 4. 10-specific language features (module _ and multi-indices operators). sprintf fmt "world" 123. Configurable: Users can change the formatting profile and configure every option in their Jul 9, 2018 · Hello everyone. sig type formatter val pp_open_box : Format. , CCFormat or Fmt) and one (meaning: me and my colleagues) often gets messy output, with box breaks and indentation not going as expected. Oct 17, 2024 · Dear everybody, a small announcement for those using OCamlformat in their projects: if you find the burden on external contributors very high, and always express “please run ocamlformat on your PR” – we’ve been in the same boat. We developed a GitHub action which automatically runs OCamlformat and pushes that on the PR. err_formatter outputs to stderr Most functions in the Format module come in two variants: a short version that operates on the current domain's standard formatter as obtained using Format. jgluuay frwg rohia qiqq hcrm bpdmtm sopxuxlf fry gefyflq ldh