Automatically generate documentation from comments in R7RS Scheme code

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2023-04-09 app: rename -I command-line flag to -w Sören Tempel
2023-04-09 app: Add help text for command-line options Sören Tempel
2023-04-09 Allow disabling warnings about unexported identifiers Sören Tempel
2023-04-09 app: Use RecordWildCards in writeDoc Sören Tempel
2023-04-02 Format: Move onId function to Util.hs and also use it for Record.hs Sören Tempel

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A sample documentation for chibi parse is available:


Tooling for inline source code documentation of Scheme code is rare. Existing tools like chibi-doc actually interpret/load the code and thus do not work if, for example, some utilized libraries are not available for chibi-scheme. To overcome this limitation scmdoc takes a different approach were the code is not interpreted and only parsed. This allows scmdoc to be applicable to different R⁷RS implementations (CHICKEN, Guile, Gambit, Racket, …) as long as the input is syntactically valid R⁷RS. Pattern matching is then performed on parsed S-expressions to format them nicely in the generated documentation (e.g. matching for procedure definitions, library definitions, …). In its essence, scmdoc is therefore a glorified pattern matcher for S-expressions.


This is currently a proof-of-concept. The R7RS parser should support the majority of the standard but is not well tested. A HTML generation backend is available and several R7RS expressions are formatted at the moment, including more complex ones like record type definitions.


This software is known to compile with GHC 9.4.4 and can be installed by running the following commands inside the repository:

$ cabal install


Unit tests are available and can be invoked using the following command:

$ cabal test

Furthermore, integration tests are available. These tests require the scmdoc binary to be available in your $PATH. Furthermore, they require Tidy to be installed. If these prerequisites are satisfied run the following command to execute these tests:

$ ./golden/


The scmdoc tool is structured around R7RS Scheme libraries. For a given Scheme source file, it extracts all library declaration which are prefixed by a doc comment. Contrary to a normal Scheme comment, a doc comment has the form ;;>. As such, scmdoc would for example recognize the following library declaration:

;;> My awesome scheme library
(define-library (sample-library)

For each recognized library, scmdoc expands all includes in the declaration and then extracts all exported and documented expressions from the library. The recognized expressions are then further processed by high-level formatters which recognize S-expressions constituting Scheme procedure definitions et cetera. These formatters are available in src/SchemeDoc/Format and essentially perform pattern matching on arbitrary S-expressions. For example, the formatter for Scheme procedure definitions roughly looks as follows:

mkProcedure :: Sexp -> Maybe Procedure
mkProcedure (List ((Id "define"):(List ((Id defid):arglst)):bodylst)) =
    -- Convert the S-expression into an algebraic data structure
    -- which represents Scheme Procedure definitions and can be
    -- formated.
mkProcedure _ = Nothing

In the future, it should be possible to also supply custom formatters to, for example, to generate documentation for definitions defined using custom macros. Apart from formatters, scmdoc also has a WiP concept of “expanders” which perform primitive comment-preserving macro expansion. This feature is presently used to expand record type definitions (define-record-type) to primitive procedure definitions which are then formatted using the procedure formatter.


The scmdoc tool generates HTML from a Scheme input defining a R7RS library. As described above, only documented S-expressions for which a documentation formatter is available are included in the generated documentation. In order to demonstrate generation of HTML documentation consider the following input file called library.scm:

;;> This is my documented library.
(define-library (math arithmetic)
  (export my-proc my-magic-constant)

  ;; This is a normal comment which is not considered by scmdoc.
    ;;> this is a hidden helper function which is not exported.
    (define my-mult *)

    ;;> my-proc multiplies the given value with two.
    (define (my-proc x)
      (my-mult x 2))

    ;;> A magic constant.
    (define my-magic-constant 42)))

In order to generate HTML documentation, using scmdoc, for this library run the following command:

$ scmdoc library.scm

Within documentation comments, it is possible to use Markdown markup.

Section Comments

Due to the lack of type information, it is difficult to meaningfully group Scheme program components. For this reason, scmdoc relies on manually inserted section comments for grouping. A section comment is a documentation comment which starts with a | character and is followed by an empty line and a normal documentation comment. The section comment corresponds to the section title, the documentation comment following it functions as the section description. For example:

;;>| Multiplication Procedures
;;> Procedures for performing multiplication.

;;> Multiply two signed values.
(define (multS x y) …)

;;> Multiply two unsigned values.
(define (multU x y) …)

This will group the procedure multS and multU into the section “Multiplication Procedures”. Every section comment consists of a section title (as indicated by ;;>|) and a mandatory section description. Each documented Scheme library should contain at least one section comment. If the Scheme library doesn’t contain any section comments, then everything is grouped under an arbitrary “Declarations” section.

Look and Feel

The HTML generated by scmdoc should be compatible with any classless CSS framework. By default, the water.css dark theme is used. A custom CSS stylesheet can be specified using the --stylesheet command-line. For more information on classless CSS frameworks refer to this blog post.

Related Work

A loose, incomplete collection of similar work on the documentation of Scheme code:


Please format all code with fourmolu. For convince, a pre-commit Git hook for checking if files are properly formated is provided in .githooks. It can be activated using:

$ git config --local core.hooksPath .githooks


This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation. Furthermore, this code presently includes the Scheme number parser from Husk Scheme which is licensed under MIT.