Writing Documentation#

FORD usage is based on projects. A project is just whatever piece of software you want to document. Normally it would either be a program or a library. Each project will have its own Markdown file which contains a description of the project. For details on some of the non-Markdown syntax which can be used with FORD, see below. Various options can be specified in this file, such as where to look for your projects source files, where to output the documentation, and information about the author. See example-project-file.md for a sample project file.

Other documentation is placed within the code. This is described in more detail below.

Indicating Documentation#

In modern (post 1990) Fortran, comments are indicated by an exclamation mark (!). FORD will ignore a normal comment like this. However, comments with two exclamation marks (!!) are interpreted as documentation and will be captured for inclusion in the output. If desired, the character(s) designating documentation can be changed. By default, FORD documentation comes after whatever it is that you are documenting, either at the end of the line or on a subsequent line. This was chosen because it was felt it is easier to make your documentation readable from within the source-code this way. This:

subroutine feed_pets(cats, dogs, food, angry)
    !! Feeds your cats and dogs, if enough food is available. If not enough
    !! food is available, some of your pets will get angry.

    ! Arguments
    integer, intent(in)  :: cats
        !! The number of cats to keep track of.
    integer, intent(in)  :: dogs
        !! The number of dogs to keep track of.
    real, intent(inout)  :: food
        !! The ammount of pet food (in kilograms) which you have on hand.
    integer, intent(out) :: angry
        !! The number of pets angry because they weren't fed.

    !...
    return
end subroutine feed_pets

looks better/more readable than:

!! Feeds your cats and dogs, if enough food is available. If not enough
!! food is available, some of your pets will get angry.
subroutine feed_pets(cats, dogs, food, angry)

    ! Arguments
    !! The number of cats to keep track of.
    integer, intent(in)  :: cats
    !! The number of dogs to keep track of.
    integer, intent(in)  :: dogs
    !! The ammount of pet food (in kilograms) which you have on hand.
    real, intent(inout)  :: food
    !! The number of pets angry because they weren't fed.
    integer, intent(out) :: angry

    !...
    return
end subroutine feed_pets

in the opinion of this author, especially with regards to the list of arguments. Since version 1.0.0 it is now possible to place documentation before the code which it is documenting. To do so, use the predocmark, which is set to > by default (it may be changed in the specify in the metadata of your project file). In the first line of your preceding documentation, use !> rather than the usual !!. This can be used on all lines of the preceding documentation if desired, but this is not necessary.

For longer blocks of documentation, it can be inconvenient to continually type the “docmark”. For such situations, the docmark_alt (set to * by default) may be used in the first line of the documentation comment. Any immediately following lines containing only a comment will then be included in the block of documentation, without needing the “docmark”. The same effect can be achieved for preceding documentation by using the predocmark_alt, set to | by default. Both of these may be changed in the project file metadata.

Legacy fixed-form FORTRAN code is now supported, using the fixed2free utility. Files with extensions .f, .for, .F, or .FOR are interpreted as fixed-form, but these settings can be changed in the project file. However, from a stylistic point of view, it is strongly recommended that free-form Fortran is used for all new code; this feature has only been added to support legacy code.

By default, FORD will preprocess any files with extensions .F90, .F95, .F03, .F08, .F15, .F, or .FOR prior to parsing them for documentation. This behaviour can be disabled or different extensions can be specified, if desired. Note that any syntax-highlighted source code which is displayed in the output will be shown in its non-preprocessed form. The default preprocessor is CPP in legacy mode (the same as used by gfortran), but arbitrary preprocessors may be specified.

Markdown#

All documentation, both that provided within the source files and that given in the project file, should be written in Markdown. In addition to the standard Markdown syntax, you can use all of the features in Python’s Markdown Extra. Other Markdown extensions automatically loaded are CodeHilite, which provides syntax highlighting for code fragments in your documentation, and Meta-Data, which is used as a way to provide extra information and/or customize behaviour. See Documentation Metadata for the syntax and what metadata you can set.

LaTeX Support#

You can insert LaTeX into your documentation, which will be rendered by MathJax. Inline math is designated by $...$, math displayed on its own line is indicated by $$...$$ or \[...\], and a numbered equation is designated by \begin{equation}...\end{equation}. Inline math will not be displayed with the traditional $...$ , as there is too much risk that dollar signs used elsewhere will be misinterpreted. You can refer back to number equations as you would in a LaTeX document. For more details on that feature, see the MathJax Documentation.

Notes and Warning Boxes#

If you want to call particular attention to a piece of information, you can use the @note markup to place it in a highlighted box:

@note
You can include any notes (or bugs, warnings, or todos) like so.
@endnote

becomes:

An example of a @note box — An example of a `@note` box#

This syntax may be used at almost any location in the documentation comment and it will include as the note’s contents anything until the first use of @endnote (provided there are no new @note or other boxes, described below, started before then). If no such @endnote tag can be found then the note’s contents will include until the end of the paragraph where the environment was activated.

There are some variations on @note boxes, which are coloured differently:

@note
@warning
@todo
@bug
@history

You can give them a custom title by putting it in quotes immediately after the tag:

@note "Custom title"
Note text
@endnote

These boxes all use the CSS class alert, as well as alert-<name> (for example, alert-note), so you can customise them if you wish. You can even add your own CSS classes, although you must also give a title in that case:

@note highlight blink "Title"
Note text
@endnote

Note that these tags are case-insensitive (which, as Fortran programmers, we’re all used to). If a note is used within the first paragraph of something’s documentation and you do not manually specify a summary, then the note will be included in the summary of your documentation. If you do not want it included, just place the note in a new paragraph of its own.

Notes can include other markdown, such as lists or code blocks, and can be used in other places such as lists – although you need to be careful about indentation in such cases.

“Include” Capabilities#

FORD uses Chris MacMackin’s Markdown-Include extension. The syntax {!file-name.md!} in any of your documentation will be replaced by the contents of file-name.md. This will be the first thing done when processing Markdown, and thus all Markdown syntax within file-name.md will be processed correctly. You can nest these include statements as many times as you like. All file paths are evaluated relative to the directory containing the project file, unless set to do otherwise.

Environment Variables#

FORD uses Chris MacMackin’s ford.md_environ extension (bundled with FORD). The syntax ${ENVIRONMENT_VAR} will be replaced by the contents of environment variable ENVIRONMENT_VAR if it is defined, or an empty string otherwise.

Aliases#

FORD allows the use of text macros or aliases to substitute for common snippets, such as URLs. These are handy for internal links in the documentation, such as to the static pages. There are three predefined macros:

|url|: the project URL
|media|: the (absolute) path to the media directory
|page|: the static page directory

You can defined additional custom aliases with the alias option.

Links#

In addition to conventional Markdown links, FORD provides its own syntax for linking to other parts of the documentation. The general syntax for this is [[component(type):item(type)]]:

component is the name of the component of your project’s code whose documentation is to be linked to. It could be a procedure, module, or anything else with its own page of documentation. This is the only item which is mandatory.
type (optional) is component’s type of Fortran construct. This is necessary if you have multiple items with the same name (such as a type and its public constructor). If multiple items with the same name exist and type is not specified then FORD’s behaviour is undefined; it will link to the first of those items which it finds. The available options are “procedure”, “subroutine”, “function”, “proc” (all of which are interchangeable and specify a procedure), “interface”, “absinterface” (both of which are for abstract interfaces), “block” (for the legacy block data program unit), and “type”, “file”, “module”, and “program” (which are self-explanatory).
item (optional) specifies an item within component which is to be linked to. The link’s target will be item’s location on component’s page. If item is not present then the colon in the link must be omitted.
type (optional, but item must also be present) is item’s type of Fortran construct. It can be used in the same manner as the component type, but has different options. These are “variable”, “type”, “constructor”, “interface”, “absinterface” (abstract interface), “subroutine”, “function”, “final” (finalization procedure), “bound” (type-bound procedure), “modproc” (module procedure in a generic interface block), and “common”. None of these options are interchangeable. If no description is given then its meaning should be self-explanatory. If you specify an option that can not exist within component (for example, if component is a module and item is “bound”) then a warning message is issued and the link is not generated.

If you have an overridden constructor a derived type, then it is strongly recommended that you specify item should you wish to link to either of them. Otherwise FORD will not know whether you are referring to the derived type itself or the interface for its constructor.

Non-Fortran Source Files#

As of version 4.5.0, FORD now offers limited support for non-Fortran source files. While it will not analyze the code within such files, it can extract documentation for the file as a whole and display it on its own page, as done for Fortran source files. An attempt will also be made to apply syntax highlighting to the contents of the file (although this may fail if non-standard file extensions are used). This may be useful for documenting build scripts or C wrappers.

To use this feature, the option extra_filetypes should be specified in the project file. It can hold multiple values, each of which should be on its own line. Entries consist of the extension for the file-type which FORD is to analyze and the comment character(s), separated by a space. FORD only supports single-line comments. An example entry of this sort is

extra_filetypes: c   //
                 sh  #
                 py  #
                 tex %

To write documentation in these files, simply place one of the usual documentation characters after the specified comment characters. Note that the default documentation marker could cause problems in source files using a “shebang” at the start.

Experimental: You can now explicitly specify the lexer for syntax highlighing by adding its name next to the comment symbol:

extra_filetypes: inc ! fortran.FortranFixedLexer

Writing Documentation

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