CSC195 2013S, Class 13: Racket Internals (1): Overview

Overview:
* About Racket
* It's Going to Seem Familiar
* Extension Basics
* Compilation
* Loading

Admin:
* You're probably busy enough this week that there is no homework!
* For what we're doing today, it's helpful to have a reference page up.
  "Inside Racket"
* Please attend next week's class for debriefing!

About Racket
* Racket is a variant of Scheme
  * Descendent of PLT Scheme
* PLT Scheme is the underlying implementation of Media Scheme
* We will be transitioning to Racket
  * And to their IDE, DrRacket
* We're going to learn to write new functions (in C) that can be called 
  from Racket (essentially, a Scheme interpreter)

It's Going to Seem Familiar
* What do I include?
* What's the boilerplate?
* Functions can take different numbers of parameters.  How do we deal 
  with that?  (The signature of the functions we write)
  * Functions have to return something.  What does the return value look like
* Declaration of variables
* How do we tell the system about our new functions?
* Once we've created the C code, how do we compile it and install it?
* Generic type!

Extension Basics
* #include <escheme.h> #include <scheme.h>
* Special type: Scheme_Object (generally pointer to)
* Three boilerplate functions
  Scheme_Object *scheme_initialize(Scheme_Environment *env)
  Scheme_Object *scheme_reload (Scheme_Environment *env)
  Scheme_Object *scheme_module_name (void)
* The new functions you design
Scheme_Object *FUNCTION(int argc, Scheme_Object *argv[])
* Adding them to the C code.  Two steps!
  * First, convert the C function to a Scheme function
  proc = scheme_make_prim_w_arity (CFUNCTION, NAME, MINARITY, MAXARITY)q
  * Next, tell the Scheme environment about the function
  scheme_add_global (NAME, proc, env)

Compilation
* Two steps!
  * Compile to .o
    raco ctool --cc
  * Link to .so
    raco ctool --ld

Loading

* The simple answer
  (load-library "whatever.so")
* More sophisticated approach coming in the future

On to Real Code
* We'll read some
* We'll write some

Strange issue: There are (at least) four names we worry about
* the name from scheme_module_name
* the name of your C function
* the name used in scheme_make_prim_w_arity
  * the name associated with the fucntion behind the scenes (for error
    reporting and such)
* the name used in scheme_make_global
  * The name you use when you call the function