[[tags: egg gmi]]

== gmi

[[toc:]]

=== Description

This egg can be used to read, manipulate, and write Gemtext, the Gemini
protocol's "default" text format.

=== Author

siiky

=== Repository

[[https://git.sr.ht/~siiky/gmi.scm]]

=== Requirements

This egg has no dependencies apart from CHICKEN itself.

=== API

==== Reading

<procedure>(gmi:read #!optional (port (current-input-port)))</procedure>

This procedure can be used to read a Gemtext document. {{port}} determines
where to read from and is optional (defaults to {{(current-input-port)}}).

The returned value is an object that may be accessed and manipulated with the
{{gmi:*}} procedures documented below.

If the input file ends in the middle of a code block, everything up to, but not
including, the code block will be returned. Additionally a string error message
will be returned as the second value.

<parameter>*strict-gemtext-headers*</parameter>

Headers in Gemtext go up to level 3. This parameter controls whether
{{gmi:read}} should read headers strictly in "compliance mode" (the default) or
more leniently. In "compliance mode", headers with level above 3 are read as
normal text rather than as headers; in the more lenient mode, headers with
level above 3 are read as headers with the corresponding level (possibly
greater than 3).

==== Manipulation

Each "feature" of the Gemtext format has a corresponding set of predicates,
constructor(s), and accessors, for convenience -- no setters/updaters have
been defined because constructors are all so simple and of so few arguments.

However, simple Scheme types are used to represent all of a Gemtext document
and its features -- for example, {{(gmi:header level title)}} is defined as
{{`(,gmi:tag/header ,level ,title)}}. This should prove useful in case the
procedures defined and exported from this egg don't suffice for your use case.

Note that constructors don't make any type checks on a feature's fields, but
predicates do!

The used terminology will be {{obj}} for any Scheme object, and a descriptive
name for parameters and Gemtext features: {{text}}, {{header}}, {{link}},
{{list}}, {{blockquote}}, {{code}}. Fields of these feature will also have a
descriptive name -- e.g. {{level}}, {{title}}, {{uri}}, {{items}}, ...

<constant>gmi:tag/header</constant>
<constant>gmi:tag/link</constant>
<constant>gmi:tag/list</constant>
<constant>gmi:tag/blockquote</constant>
<constant>gmi:tag/code</constant>

The tag constant of each Gemtext feature, except for plain text -- more next.

<procedure>(gmi:text? obj)</procedure>
<procedure>(gmi:text text)</procedure>

This represents "normal text". No encapsulation is used here, text is
represented as the string of that text itself. {{gmi:text?}} is an alias of
{{string?}} and {{gmi:text}} is the unary identity function.

<procedure>(gmi:header? obj)</procedure>
<procedure>(gmi:header level title)</procedure>
<procedure>(gmi:header:level header)</procedure>
<procedure>(gmi:header:text header)</procedure>

{{level}} is a fixnum and {{title}} a string.

For a header created by {{gmi:read}}, if {{*strict-gemtext-headers*}} is truthy
(the default), then {{(<= 1 level 3)}}; otherwise {{(<= 1 level)}}.

<procedure>(gmi:link? obj)</procedure>
<procedure>(gmi:link uri text)</procedure>
<procedure>(gmi:link:uri link)</procedure>
<procedure>(gmi:link:text link)</procedure>

{{uri}} and {{text}} are strings. Similarly to code blocks, the {{text}} field
of a link with no alt-text is an empty string.

<procedure>(gmi:list? obj)</procedure>
<procedure>(gmi:list* items)</procedure>
<procedure>(gmi:list . items)</procedure>
<procedure>(gmi:list:items list)</procedure>

{{items}} as returned by {{gmi:list:items}} is a Scheme list of all the items
(each of them a string) of the (Gemtext) list.

<procedure>(gmi:blockquote? obj)</procedure>
<procedure>(gmi:blockquote text)</procedure>
<procedure>(gmi:blockquote:text blockquote)</procedure>

{{text}} is a string.

Each blockquote object represents a single textual line. Several textual
(blockquote) lines result in several blockquote objects even if not separated
by any blank lines.

<procedure>(gmi:code? obj)</procedure>
<procedure>(gmi:code* lines)</procedure>
<procedure>(gmi:code alt-text . lines)</procedure>
<procedure>(gmi:code:text code)</procedure>
<procedure>(gmi:code:lines code)</procedure>

{{alt-text}} is a string and {{lines}} is a Scheme list of strings. Similarly
to links, the {{alt-text}} field of a code block with no alt-text is an empty
string.

The first element of the {{lines}} argument given to {{gmi:code*}} must be the
alt-text, not the first line of code! The first line of code should be the
second element of {{lines}}.

==== Writing

<procedure>(gmi:write gmi #!optional (port (current-output-port)))</procedure>
<procedure>(gmi:write1 elem #!optional (port (current-output-port)))</procedure>

{{gmi:write}} may be used to write a Gemtext document, represented by {{gmi}}.

{{gmi:write1}} may be used to write a Gemtext element, {{elem}}, such as a
header, a list, &c. This procedure takes care of adding the necessary newlines,
no extra work required.

{{port}} determines where to write to and is optional (defaults to
{{(current-output-port)}}).

=== Examples

If you save the following Gemtext document:

<enscript>
# Factorial

There are two steps to compute the factorial of a number:

* Compute the list of integers from 1 up to the number
* Multiply all the integers of the list

=> https://en.wikipedia.org/wiki/Factorial
=> gemini://gemi.dev/cgi-bin/wp.cgi/view?Factorial Factorial (Gemipedia)

## Haskell code

Here's the code in Haskell:

```hs
fact n = prod [1..n]
```
</enscript>

And run this code with that file as stdin:

<enscript highlight="scheme">
(import gmi)
(write (gmi:read))
</enscript>

You get the following output:

<enscript highlight="scheme">
'((gmi:header 1 "Factorial")
  ""
  "There are two steps to compute the factorial of a number:"
  ""
  (gmi:list "Compute the list of integers from 1 up to the number"
            "Multiply all the integers of the list")
  ""
  (gmi:link "https://en.wikipedia.org/wiki/Factorial" "")
  (gmi:link "gemini://gemi.dev/cgi-bin/wp.cgi/view?Factorial" "Factorial (Gemipedia)")
  ""
  (gmi:header 2 "Haskell code")
  ""
  "Here's the code in Haskell:"
  ""
  (gmi:code "hs"
            "fact n = prod [1..n]"))
</enscript>

=== License

  This is free and unencumbered software released into the public domain.
  
  Anyone is free to copy, modify, publish, use, compile, sell, or
  distribute this software, either in source code form or as a compiled
  binary, for any purpose, commercial or non-commercial, and by any
  means.
  
  In jurisdictions that recognize copyright laws, the author or authors
  of this software dedicate any and all copyright interest in the
  software to the public domain. We make this dedication for the benefit
  of the public at large and to the detriment of our heirs and
  successors. We intend this dedication to be an overt act of
  relinquishment in perpetuity of all present and future rights to this
  software under copyright law.
  
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
  IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  OTHER DEALINGS IN THE SOFTWARE.
  
  For more information, please refer to <http://unlicense.org>

=== Version History

==== 0.0.1 (2022/10/28)

* Initial release.

==== 0.0.2 (2022/10/28)

* Make CHICKEN imports explicit.

==== 0.0.3 (2023/01/30)

* Remove dead code.

==== 0.0.4 (2023/02/03)

* Change underlying symbol tags;
* Add {{gmi:write}} and {{gmi:write1}}.

==== 0.0.5 (2023/02/03)

* Import {{define-constant}} from {{(chicken base)}}.

==== 0.0.6 (2023/02/06)

* Export {{gmi:tag/*}}.

==== 0.0.7 (2023/02/08)

* Detect when an input file ends in the middle of a code block and return an
  error message as a second value.

==== 0.0.8 (2024/12/10)

* Add support for CHICKEN 6.