A static site generator
+when I decided to start blogging, it was mostly for me to learn and remember all tech thing I learnt throughout time.
+I also want to explore a wide diversity of technology, not focus on a particular one.
+Hence to start blogging, I obviously needed a static site generator.
+Many of them exist already, like Hugo for example, however rewriting one from scratch is typically the kind of exercise I want to throw myself into.
+The advantage of a static site is clearly its loading speed : a simple html file, combined with a small licked css, and a whole new blog is born
+Anyway, writing this static site generator from scratch is also the perfect excuse to explore a not so widely know technology to manipulate text files.
+Introduction to AWK
+AWK, from the intials of its creator, is an old an powerful text file maniulation. Syntactically close to C, it is a scripting language to manipulation text entries.
+Its [wikipedia page](https://en.wikipedia.org/wiki/AWK) sums up nicely its story.
+I thought it was clever to use is for a site generator, to parse markdown files and generate html ones.
+However, according to this [listing](https://jamstack.org/generators/) of static site generator programs, another one has had the same idea.
+Hence, the following, as well as my code is heavily inspired by [Zodiac](https://github.com/nuex/zodiac) (even though the repo has not been touched for 8years).
+Parsing markdown
+Following the official [syntax](https://daringfireball.net/projects/markdown/syntax), is a good start for a parser.
+AWK works as follow : it takes an optional regex and execute some code between bracket, as a function, at each line of the text input.
+For example :
+/^#/ {
+ print "" $0 "
"
+}
+
+Although `$n` refers to the n-th records in the line (according to a delimiter, like in a csv), the special `$0` refers to the whole line.
+In this case, for each line starting with `#`, awk will print (to the standard output), `
[content of the line]
`. +This is the beginning to parse headers in markdown.
+However, by trying this, we immediatly see that `#` is part of the whole line, hence it also appear in the html whereas it sould not.
+AWK has a way to prevent this, as it is a complete scripting language, with built-in functions, that enable further manipulations.
+/^#/ {
+ print "" substr($0, 3) "
"
+}
+
+In the example above, as per the [documentation](https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#index-substr_0028_0029-function)
+it returns the subtring of `$0` starting at 3 (1 being `#` and 2 the whitespace following it) to the end of the line.
+Now this is better, but we now are able to generalized it to all headers. Another function, `match` can return the number of char matched by a regex,
+and allows the script to dynamically determine which depth of header it parses :
+/^#+ / {
+ match($0, /#+ /);
+ n = RLENGTH;
+ print "" substr($0, n + 1) " "
+}
+
+Reproducing this technique to parse the rest proves to be difficult, as lists for example, are not contained in a single line, hence
+how to know when to close it with `` or ``
+Introducing a LIFO stack
+Since according to the markown syntax, it is possible to have nested blocks such as headers and lists withing blockquotes, or lists withing lists, I came with the simple idea to track to current environnement in a stack in AWK.
+Turns out it came out to be easy, I only needed a pointer to track the size of the lifo, a fonction to push an element, an another one to pop one out :
+BEGIN {
+ env = "none"
+ stack_pointer = 0
+ push(env)
+}
+
+# Function to push a value onto the stack
+function push(value) {
+ stack_pointer++
+ stack[stack_pointer] = value
+}
+
+# Function to pop a value from the stack (LIFO)
+function pop() {
+ if (stack_pointer > 0) {
+ value = stack[stack_pointer]
+ delete stack[stack_pointer]
+ stack_pointer--
+ return value
+ } else {
+ return "empty"
+ }
+}
+
+The stack does not have to be strictly declared. The value of inside the LIFO correspond to the current markdown environment.
+This is a clever trick, because when I need to close an html tag, I use the poped element between a `` instead of having a matching table.
+I also used a simple `last()` function to return the last pushed value in the stack without popping it out :
+# Function to get last value in LIFO
+function last() {
+ return stack[stack_pointer]
+}
+
+This way, parsing lists became trivial :
+# Matching unordered lists
+/^[-+*] / {
+ env = last()
+ if (env == "ul" ) {
+ # In a unordered list block, print a new item
+ print "" substr($0, 3) " "
+ } else {
+ # Otherwise, init the unordered list block
+ push("ul")
+ print "
+- " substr($0, 3) "
"
+ }
+}
+
+I believe the code is pretty self explanatory, but when the last environement is not `ul`, then we enter this environement.
+This translates as pushing it to the stack.
+Otherwise, it means we are already reading a list, and we only need to add a new element to it.
+Parsing the simple paragraph and ending the parser
+I showed examples of lists and headers, but it works the same way for code blocks, blockquotes, etc.. Only the simple paragraph is different :
+it does not start with a specific caracter. That is, to match it, we match everything that is not a special character.
+I have no idea if this is the best solution, but so far it proved to work:
+# Matching a simple paragraph
+!/^(#|\*|-|\+|>|`|$| | )/ {
+ env = last()
+ if (env == "none") {
+ # If no block, print a paragraph
+ print "" replaceEmAndStrong($0) "
"
+ } else if (env == "blockquote") {
+ print $0
+ }
+}
+
+AS `BEGIN`, AWK provide the possibilty to execute code at the very end of the file, with the `END` keyword.
+Naturally we need to empty the stack and close all html tags that might have been opened during the parsing.
+It only is a while loop, until the last environement is "none", as it way initiated :
+END {
+ env = last()
+ while (env != "none") {
+ env = pop()
+ print ""
+ env = last()
+ }
+}
+
+This way we are able to simply parse markdown and turn it into an HTML file.
+Of course I am aware that is lacks emphasis, strong and code within a line of text.
+However I did implement it, but maybe it will be explained in another edit of this post.
+Nonetheless the code can still be consulted on [github](https://github.com/SiwonP/bob).
+A testing suite for markdown parser
+Having a markdown parser is cool, having one well tested id better.
+I embarked in writing a testing suite for markdown parsers. I wanted it to be generic, meaning you only had to provide a parsing program,
+that takes markdown in the standard input, and returns html in the standard output.
+All tests would be provided by the test suite.
+