* The Sex language

#+NAME: the Sex logo
#+ATTR_HTML: :width 300px
[[sex.png][file:./sex.png]]

Sex is a S-expressions language. Sex is written in Chicken, which is a
[[https://call-cc.org][R5RS Scheme]].
Sex is statically typed, compiled general purpose language.

* Compilation
First, get yourself a Chicken, then, some Chicken deps. You also will
need a C compiler.

** Install Chicken Eggs
Tip: there's a way to make Chicken install eggs non-globally. You need
to export ~CHICKEN_INSTALL_REPOSITORY~ and ~CHICKEN_REPOSITORY_PATH~
environment variables. Refer to the documentation for more info:
https://wiki.call-cc.org/man/5/Extension%20tools#changing-the-repository-location

~chicken-install `cat dependencies.txt`~

** Compilation
~make~

* Usage
** Summary
#+begin_src
Usage: sexc [options] filename [-- options-for-c-compiler]
Options:
 --c-compiler=ARG         Select C compiler. Defaults to value of SEX_CC
                          environment variable, or if it is empty, to cc
 -c, --compile-object     Compile object file instead of executable program
 -C, --preprocess         Emit C code
 --public-interface       Get module's public interface
 -h, --help               Show this help
 -m, --macro-expand       Emit macro-expanded semantically processed Sex code
                          (sort of IR). May be useful for debugging
 -o, --output=ARG         Write output to file. Default file name is a.out.
                          If -E or -m options are provided, defaults to stdout
#+end_src
** Compiling Hello World
#+begin_src shell
sexc ./examples/hello-world.sex -o hello
#+end_src

That's it. Now you should have executable named ~hello~ in your
directory. Sex uses C under the hood, the default C compiler is ~cc~,
but you can pass any using ~--c-compiler~ option, or by setting
~SEX_CC~ environment variable.

** Example
An example of Sex source:
#+begin_src scheme
(include stdio.h)

(pub fn main ((argc int) (argv  [* const char])) int
  (puts "Hello from Sex!")
  (var name [char 512])
  (puts "What is your name?")
  (scanf "%s" (cast (& name) (* char)))
  (printf "Hello, %s!\n" name)
  (return 0))
#+end_src

Compile and run:
#+begin_src shell
~/dev/sex $ ./sexc ./example/hello-world.sex -o hello-world
~/dev/sex $ ./hello-world
Hello from Sex!
What is your name?
Alex
Hello, Alex!
#+end_src

* Features
** Full C interoperability
Just ~(include "Your/Favourite/Library.h")~ and use it as you would
have is C.

*** Auto kebabification
For hardcore fans of traditional Lisp naming convention,
Sex offers automatic kebabification of all symbols, i.e. no more
ugly ~GL_ARRAY_BUFFER~ s in your code, they may be written in their
proper form: ~GL-ARRAY-BUFFER~.

** Modules
Each source file is a module. Module can provide public interface and
be imported by using ~(import path/to/module)~ expression. Module
search path consists of two parts: first is relative to the source
being compiled location, and the second is ~SEX_MODULE_PATH~
environment variable.

Module's public interface consists of everything declared
~pub~. Structures, function, macros, types, variables can be
public.

** Syntactic macros
Sex has support for syntactic macros. Macro definitions look like
functions: they have a name, an argument list and a body. Macro should
return Sex code.

*** Examples:
**** Structure with templated value type
#+begin_src scheme
(pub defmacro (list-T type)
  (let ((list-type (cat 'list- type)))
    `(struct ,list-type
       ((value ,type)
        (next (* ,list-type))))))

(list-T int)
#+end_src
->
#+begin_src scheme
(struct list_int
 ((value int)
  (next (* list_int))))
#+end_src

**** Wrapper for checking return codes
#+begin_src scheme
(pub defmacro (check-sdl-return call message ret-code)
  `(if (< 0 ,call)
       (begin
         (puts ,message)
         (return ,ret-code))))

(pub fn init () int
  (check-sdl-return
    (SDL-Init SDL-INIT-VIDEO) "Failed to initialize SDL" 1)
...)
#+end_src
->
#+begin_src scheme
(pub fn init () int
  (if (< 0 (SDL_Init SDL_INIT_VIDEO))
    (begin (puts "Failed to initialize SDL") (return 1)))
  ...)
}
#+end_src

** Use an established environment for development
As Sex is S-expressions, you always have Emacs with paredit as your
best option.

*** sex-mode.el
To harness the power of sex-mode, add the following lines to your
~$HOME/.config/emacs/init.el~:
#+begin_src emacs-lisp
(use-package sex-mode
  :load-path "/path/to/sex"
  :mode ("\\.sex\\'"))
#+end_src