[[tags: egg]]
[[toc:]]
== chalk
Simple hahn-style in-source documentation

=== Introduction
Chalk attempts to be a simpler alternative to Chicken 4's
[[https://wiki.call-cc.org/eggref/4/hahn|hahn]] +
[[https://wiki.call-cc.org/eggref/4/hahn-utils|hahn-utils]], generating wiki
output with support for procedure, variables, syntax, modules, include files,
and egg files. It tries to be as basic as possible, performing almost no code
analysis and no evaluation, while making it easy to generate documentation from
one or more files.

The following is hahn's fibonacci example, rewritten for chalk. Note key
differences: The example is simply a string (and therefore not evaluated),
whith the option of a {{@pre}} or {{@post}} caption.

<enscript highlight="scheme">
(define (fibonacci n)
  @("Computes the nth [[http://en.wikipedia.org/wiki/Fibonacci_number|Fibonacci]].
This naïve algorithm runs in ''O(2^n)''; using e.g. memoization, we could bring
it down to ''O(n)''."
    (n "The nth number to calculate")
    (@to "integer")
    (@example
     (@pre "For example, computing the 6th Fibonnaci number (starting from 0)")
     "(fibonacci 6) ; => 8"))
  (case n
    ((0) 0)
    ((1) 1)
    (else (+ (fibonacci (- n 1))
             (fibonacci (- n 2))))))
</enscript>

Which produces the following wiki output:

<procedure>(fibonacci n) → integer</procedure>
Computes the nth [[http://en.wikipedia.org/wiki/Fibonacci_number|Fibonacci]].
This naïve algorithm runs in ''O(2^n)''; using e.g. memoization, we could bring
it down to ''O(n)''.

; n : The nth number to calculate

For example, computing the 6th Fibonnaci number (starting from 0)
<enscript highlight="scheme">
(fibonacci 6) ; => 8
</enscript>

=== Syntax

Most expressions of the following form can be documented to varying degrees of
automation, where {{SIGNATURE}} can be a pair (as in a procedure definition).

<enscript>
(DEFINE SIGNATURE BODY ...)
</enscript>

Documentation entails inserting a docexpr of the following form before the
{{BODY}}.

<enscript>
@("Description" ... [OPTION] ...)
</enscript>

Multiple top-level strings in the docexpr are turned into separate wiki paragraphs.

==== Variables
Variables are documented as follows, ignoring potentially disastrous rounding practices:
<enscript highlight="scheme">
(define pi @("The ratio of a circle's circumference to its diameter.") 3.14)
</enscript>

The special tag {{@internal}} can be used to suppress output, and is useful for
documenting unexported variables internally:

<enscript highlight="scheme">
(define counter
  @("How many times thing has happened."
    (@internal)))
</enscript>

==== Procedures

Procedures are documented similarly, but can contain the tags, {{@to}}, and
{{@example}}, as well as listing function parameters:

<enscript highlight="scheme">
(define (foobar a b)
  @("Does baz."
    (a "An input")
    (b "Another input")
    (@to integer)
    (@example
     (@pre "For example, to do baz with foobar:")
     "(foobar blarg arg) ; => 4"))
  (baz))
</enscript>

In the case of procedures defined as variables, chalk considers them variables
by default, using the function name as a signature. In either case, you can
override the default signature with the tag {{@sig}}, and you can specify that
it is indeed a procedure as follows:

<enscript highlight="scheme">
(define function?
  @(fn "This is definitely a function"
       (@sig (function? a b c)))
  (lambda () (print "bar")))
</enscript>

You can specify that a variable definition is a procedure with any of {{fn}},
{{proc}}, {{function}}, or {{procedure}} in the first position of the docexpr.

Tags behave as follows:

; @to : A string or expression to be inserted as {{→ expr}}
; @example : A string to be enscripted with scheme highlighting, with optional {{@pre}} or {{@post}} caption.
; @sig : A string or expression that override the procedure signature
; @internal : Suppress output, documented for internal use.

==== Syntax definitions

Syntax definitions accept the same tags and is defined equivalently to
procedures, provided that it is is defined using {{define-syntax}}. The
{{@sig}} tag is especially useful for specifying syntax usage, since chalk
won't automatically detect the signature. Here's a rather silly example:

<enscript highlight="scheme">
(define-syntax hello
  @("Hello there!"
    (@sig (hello a b c)))
  (syntax-rules ()
    ((_ a b c)
     "Hello there!")))
</enscript>

For syntax defined otherwise, you can specify that it is syntax like so:

<enscript highlight="scheme">
(define-syntax-rule (hello a b c)
  @(syntax "Hello")
  "Hello there")
</enscript>

You can specify that a definition is syntax with either {{syntax}} or {{macro}}
in the first position of the docexpr.

==== Records

Currently, two types of record definitions are supported - {{define-record}}
and {{define-record-type}} from {{chicken.base}}. Records can be documented
internally by specifying a {{@internal}} file, and they accept one more tag
{{@full}}. When specified, it generates a list of all of the procedures
associated with that record definition. Otherwise, only the record name is
documented, and procedure documentation can be added manually.

For example:

<enscript highlight="scheme">
(define-record point
  @("A point"
    (@full))
  x y)
</enscript>

Produces the following output:

<record>point</record>
<procedure>(make-point x y)</procedure>
<procedure>point?</procedure>
<procedure>point-x</procedure>
<procedure>point-y</procedure>
A point

==== Top-level documentation

A docexpr outside of a definition can be used to insert arbitrary text.
Additionally, the following top-level tags are supported:

; script : Generate an enscript segment, with optional highlight tag. Can contain multiple strings.

<enscript highlight="scheme">
@(script
  (@highlight "scheme")
  "(print \"hello\")"
  "(print 4)")
</enscript>

In addition to the {{@highlight}} tag, a caption can be inserted before or
after a script using the tags {{@pre}} and {{@post}}.

; heading, title, == : A title

<enscript highlight="scheme">
@(== "My egg")
</enscript>

Various subheadings:

; subheading, subtitle, === :
; subsubheading, subsubtitle, ==== :
; subsubsubsubheading, subsubsubsubtitle, ===== :

; deflist : A definition list such as this one

<enscript highlight="scheme">
@(deflist
   (key "value")
   (definitionless-term)
   (term "definition"))
</enscript>

Lists and tables are not currently supported, but are planned for the future.
In the meantime, unsupported forms of wiki syntax can be inserted literally
using a top-level docexpr.

=== Compiling and running programs

To compile a scheme file containing chalk special syntax, you can use {{-X
chalk}}. For script usage (e.g. with {{csi -s}}), you can use {{import chalk}}.

=== Chalk program usage

The chalk program generates output to stdout or a specified output file based
on the given input file(s), and optionally: a {{.egg}} file, a
{{.release-info}} file, and/or a {{LICENSE}} file. For more info, see {{chalk --help}}:

<enscript>
Usage: chalk [OPTION]... [FILE]...
 -h, --help               Print usage
 -o, --output=FILE        Write to file
 -i, --ignore-egg         Ignore .egg file
 -r, --ignore-release     Ignore .release-info file
 -n, --no-toc             Don't add a toc
 -e, --email=EMAIL        Include EMAIL with author
 -H, --head=FILE          File to add to beginning of documentation
 -P, --prologue=FILE      File to add after synopsis
 -E, --epilogue=FILE      File to add before maintainer info
 -T, --tail=FILE          File to add to end of documentation
 -L, --no-license         Don't insert a license file
 -l, --license=FILE       File to use as license (defaults to LICENSE if unspecified)
 -m, --module-headers     Create === Module-name headers
 </enscript>

A {{.release-info}} file can contain optional comments following {{release}}
expressions (on the same line), which are used as version descriptions when
generating a version history section of the documentation, for example:

<enscript highlight="scheme">
(uri targz "https://example-url.com")
(release "0.3.1") ; Fixes bug
(release "0.3.0") ; Adds feature
(release "0.2.0")
(release "0.1.0") ; Initial version
</enscript>

=== Full Example

See the [[https://code.dieggsy.com/icu/tree/|ICU egg source code]] and
[[https://wiki.call-cc.org/eggref/5/icu|documentation]] for a full example of a
project using chalk.

=== Author
Diego A. Mundo

=== Version History

; 0.3.5 : Add support for {{define-library}}
; 0.3.4 : Allow multiple strings as description
; 0.3.3 : Reduce line spacing, change license options
; 0.3.2 : Add multi-line script support
; 0.3.1 : Fix bug: release-info not ignored on ignore-egg
; 0.3.0 : Add support for records and syntax
; 0.2.0 : Add {{@example}}, listed function parameters, script caption
; 0.1.0 : Initial version

=== License

 Copyright (c) 2020 Diego A. Mundo
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted (subject to the limitations in the disclaimer
 below) provided that the following conditions are met:
 
      * Redistributions of source code must retain the above copyright notice,
        this list of conditions and the following disclaimer.
 
      * Redistributions in binary form must reproduce the above copyright
        notice, this list of conditions and the following disclaimer in the
        documentation and/or other materials provided with the distribution.
 
      * Neither the name of the copyright holder nor the names of its
        contributors may be used to endorse or promote products derived from
        this software without specific prior written permission.
 
 NO EXPRESS OR IMPLIED LICENSES TO ANY PARTY'S PATENT RIGHTS ARE GRANTED BY THIS
 LICENSE. THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
 THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.