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anil.recoil.org
1opam-version: "2.0"
2maintainer: "Gabriel Radanne <drupyog@zoho.com>"
3authors: [ "Thomas Gazagnaire"
4 "Anil Madhavapeddy"
5 "Dave Scott"
6 "Thomas Leonard"
7 "Gabriel Radanne" ]
8homepage: "https://github.com/mirage/functoria"
9bug-reports: "https://github.com/mirage/functoria/issues"
10dev-repo: "git+https://github.com/mirage/functoria.git"
11doc: "https://mirage.github.io/functoria/"
12license: "ISC"
13tags: ["org:mirage"]
14
15build: [
16 ["jbuilder" "subst" "-p" name] {dev}
17 ["jbuilder" "build" "-p" name "-j" jobs]
18 ["jbuilder" "runtest" "-p" name "-j" jobs] {with-test}
19]
20depends: [
21 "ocaml" {>= "4.03"}
22 "jbuilder" {>= "1.0+beta20"}
23 "base-unix"
24 "cmdliner" {>= "0.9.8" & < "1.1.0"}
25 "rresult"
26 "astring"
27 "fmt" {< "0.8.10"}
28 "ocamlgraph"
29 "logs"
30 "bos"
31 "fpath"
32 "alcotest" {with-test}
33]
34synopsis: "A DSL to organize functor applications"
35description: """
36[](https://travis-ci.org/mirage/functoria)
37[](https://mirage.github.io/functoria/index.html)
38
39## What is this for?
40
41Functoria is a DSL to describe a set of modules and functors, their types and how to apply them in order to produce a complete application.
42
43The main use case is mirage. See the [mirage][] repository for details.
44
45## How to write a configuration file?
46
47There are numerous examples of configuration files in [mirage-skeleton][]. Most of them should be fairly general and understandable, even outside the context of mirage. We can distinguish two parts in a `config.ml`: Defining new modules and using them.
48
49In order to define a new module, we use the `foreign` function. Among its various arguments, it takes a module name and a type. The type is assembled with the DSL's combinators and the `@->` operator, which symbols a functor arrow.
50
51```ocaml
52let main = foreign "Unikernel.Main" (console @-> job)
53```
54
55Here, we declare the functor `Unikernel.Main` that takes a module that should be a `console` and returns a module that is a `job`. It is up to the user to ensure that the declaration matches the implementation (or be punished by a compiler error later on). If the declaration is correct, everything that follows will be.
56
57We can now use this declaration:
58
59```ocaml
60let () = register "console" [main $ default_console]
61```
62
63Here, we register a new application with the `register` function. This function should only be called once and takes as argument the name of the application and a list of jobs. We use the `$` operator to apply the functor `main` (aka `Unikernel.Main`) to the default console.
64
65Now that everything is ready, you can use the `configure` subcommand!
66
67### What is a job?
68
69A job is a module containing a function `start`. This function will receive one argument per functor argument and one per dependency, in this order. `foreign` assumes the function `start` returns `unit`.
70
71### Defining new keys
72
73A key is composed of:
74
75- _name_ : The name of the value in the program.
76- _description_ : How it should be displayed/serialized.
77- _stage_ : Is the key available only at runtime, at configure time or both?
78- _documentation_ : It is not optional so you should really write it.
79
80Consider a multilingual application: we want to pass the default language as a parameter. We will use a simple string, so we can use the predefined description `Key.Desc.string`. We want to be able to define it both at configure and run time, so we use the stage `` `Both``. This gives us the following code:
81
82```ocaml
83let lang_key =
84 let doc = Key.Arg.info
85 ~doc:"The default language for the application." [ "l" ; "lang" ]
86 in
87 Key.create "language" @@ Key.Arg.(opt ~stage:`Both string "en" doc)
88```
89
90Here, we defined both a long option `--lang` and a short one `-l` (the format is similar to the one used by [Cmdliner][cmdliner]).
91In the application code, the value is retrieved with `Key_gen.language ()`.
92
93The option is also documented in the `--help` option for both the `configure` subcommand (at configure time) and `./my_application` (at startup time).
94
95```
96 -l VAL, --lang=VAL (absent=en)
97 The default language for the application.
98```
99
100[cmdliner]: http://erratique.ch/software/cmdliner
101
102### Using switching keys
103
104We can do much more with keys: we can use them to switch implementation at configure time. Imagine we want to completely change some implementation based on the language. Finns are special snowflakes, they deserve their special application!
105
106First, we have to compute a boolean value from `lang`:
107
108```ocaml
109let is_fi = Key.(pure ((=) "fi") $ value lang_key)
110```
111
112We can use the `if_impl` combinator to choose between two implementations depending on the value of the key:
113
114```ocaml
115let dynamic_storage =
116 if_impl is_fi
117 finnish_implementation
118 not_finnish_implementation
119```
120
121This distinction will be visible using the `describe` subcommand and a dot diagram is available with the `--dot` option!
122
123## Internals
124
125### Phases
126
127Configuration is separated into phases:
128
1291. Specialized DSL keys
130 The specialized DSL's keys (along with functoria's keys) are resolved.
1312. Compilation and dynlink of the config file.
1323. Registering.
133 When the `register` function is called, the list of jobs is recorded and
134 immediately transformed into a graph.
1354. Switching keys and tree evaluation.
136 The switching keys are the keys inside the [If].
137 Those keys are resolved and the graph is simplified. At this point,
138 the actual modules used are fully known.
139 Note: for the `describe` command, Only _partial_ evaluation is done, which
140 means decision nodes are resolved only if the value was given on the command
141 line, disregarding default values.
1425. Full Key resolution.
143 Once the actual modules are known, we can resolve all the keys and figure out
144 libraries and packages.
1456. Dependency handling, configuration and code emission.
146
147Phases 1. to 4. are also applied for the `clean` command.
148
149
150
151[mirage]: https://github.com/mirage/mirage
152[mirage-skeleton]: https://github.com/mirage/mirage-skeleton"""
153url {
154 src:
155 "https://github.com/mirage/functoria/releases/download/2.2.1/functoria-2.2.1.tbz"
156 checksum: [
157 "sha256=e2c883d5a0a2c3cea59cffa9989c5ee78259aee9a199048cb730d19076e668c5"
158 "md5=ec768d65f4070dd76c369b4a32a1ac32"
159 ]
160}
161available: opam-version >= "2.2.0"
162flags: deprecated