Convert Gemtext to HTML

Question

Gemtext is a very simple markup format used by the alternative web protocol Gemini. Write a Gemtext to HTML converter.

From the Wiki:

A line of text is a paragraph, to be wrapped by the client. It is is independent from the lines coming before or after it.

A list item starts with an asterisk and a space. Again, the rest of the line is the line item, to be wrapped by the client.

A heading starts with one, two, or three number signs and a space. The rest of the line is the heading.

A link is never an inline link like it is for HTML: it’s simply a line starting with an equal-sign and a greater-than sign: “=>”, a space, an URI, and some text. It could be formatted like a list item, or like a paragraph. Relative URIs are explicitly allowed.

Example:

# This is a heading 
This is the first paragraph.
* a list item
* another list item 
This is the second paragraph.
=> http://example.org/ Absolute URI
=> //example.org/ No scheme URI
=> /robots.txt Just a path URI
=> GemText a page link

This should produce this HTML tree (just the equivalent tree, not the exact formatting):

EDIT you don't need the <ul> tags to produce valid HTML

<h1>This is a heading</h1>
<p>This is the first paragraph.</p>
<li>a list item</li>
<li>another list item</li>
<p>This is the second paragraph.</p>
<a href="http://example.org/">Absolute URI</a>
<a href="//example.org/">No scheme URI</a>
<a href="/robots.txt">Just a path URI</a>
<a href="GemText">a page link</a>

All text must pass through. All of <>"& should be converted to HTML entities, even if they don't confuse browsers, to be safe

EDIT: For the sake of this question, you don't have to do 2nd and 3rd level headings

This is code-golf so the shortest code in bytes wins

Answer 1

Perl 5 (-p), 132 bytes

s,^((#)|(\*)|=> (\S+)|) *(.*?) *$,$t=$2?h1:$3?li:$4?a:p;"<$t".($4&&qq( href="$4")).">".($5=~s~[<>"&]~"&#".(ord$&).";"~ger)."</$t>",e

Try it online!

Another 132 bytes

s-^([#*]|=> (\S+)|) *(.*?) *$-"<".($t=(p,a,li,h1)[ord($1)%4]).($2&&qq( href="$2")).">".($3=~s~[<>"&]~"&#".(ord$&).";"~ger)."</$t>"-e

Answer 2

Java + Android, 227 206 bytes

l->l.map(s->android.text.Html.escapeHtml(s).replaceAll("^# (.*)","<h1>$1</h1>").replaceAll("^\\* (.*)","<li>$1</li>").replaceAll("^=&gt; (.*?) (.*)","<a href='$1'>$2</a>").replaceAll("^[^<].*","<p>$0</p>"))

Accepts a Stream of lines as input and returns a Stream of lines.

Try it online!

Saved 21 bytes thanks to Olivier Grégoire

Explanation

l->l.map(
   s->android.text.Html.escapeHtml(s) //Escape line using Android utility class
   .replaceAll("^# (.*)","<h1>$1</h1>")
   //Match headers 
   .replaceAll("^\\* (.*)","<li>$1</li>")
   //Match list items
   .replaceAll("^=&gt; (.*?) (.*)","<a href='$1'>$2</a>")
   //Match links (> is &gt; after being escaped)
   .replaceAll("^[^<].*","<p>$0</p>")
   //If string does not start with <, then nothing has been replaced,
   //so enclose entire line in paragraph element
)

Answer 3

Retina 0.8.2, 104 103 bytes

&
&
"
"
>
>
<
&lt;
m`^
<p>
p>(#+)
h$.1>
p>\*
li>
p>=&gt; (\S+)
a href="$1">
<(\w+).*
$&</$1>

Try it online! Works with multiple headers. Edit: Saved 1 byte thanks to @OlivierGrégoire. Explanation:

&
&
"
"
>
>
<
&lt;

HTML encode everything.

m`^
<p>

Assume each line is a paragraph.

p>(#+)
h$.1>
p>\*
li>
p>=> (\S+)
a href="$1">

Fix up headings, lists and links.

<(\w+).*
$&</$1>

Add closing tags.

Answer 4

sed 4.2.2, 160 bytes

s!&!&!g
s!<!\&lt;!g
s!>!\&gt;!g
s!"!\&#34;!g
ta
:a
s!^*\(.*\)!<li>\1</li>!
s!^#\(.*\)!<h1>\1</h1>!
s!=&gt; \([^ ]*\)\(.*\)!<a href="\1">\2</a>!
t
i<p>
a</p>

Try it online!

Answer 5

JavaScript (Node.js), 243 215 210 194 193 191 bytes

n=>n.split`
`.map(e=>`<${t={'#':'h1','*':'li','=>':'a'}[(s=e.split` `)[0]]||'p'}${a=t<'b'?` href="${s[1]}"`:''}>${s.slice(2-!a).join` `.replace(/./g,c=>`&#${Buffer(c)[0]};`)}</${t}>`).join`
`

Try it online!

As with most of my longer answers, I will golf this gradually.

Produces unreadable HTML, but still containing the same text. If this is disallowed, let me know and I will roll it back.

-16 bytes thanks to @A Username

Answer 6

AWK, 171 bytes

awk '{if($1=="#"){$1="<h1>";$0=$0"</h1>"}else if($1=="*"){$1="<li>";$0=$0"</li>"}else if($1=="=>"){$1="<a href=\""$2"\">";$0=$0"</a>"}else{$1="<p>";$0=$0"</p>"}{print$0}}'

I'm learning AWK so probably can be done better.
Bugs:

• There are spaces after the opening tags
• Doesn't remove the URL (I've tried doing $2="", but it breaks the lines)