1 //: You guessed right: the '000' prefix means you should start reading here.
  2 //:
  3 //: This project is set up to load all files with a numeric prefix. Just
  4 //: create a new file and start hacking.
  5 //:
  6 //: The first few files (00*) are independent of what this program does, an
  7 //: experimental skeleton that will hopefully make it both easier for others to
  8 //: understand and more malleable, easier to rewrite and remould into radically
  9 //: different shapes without breaking in subtle corner cases. The premise is
 10 //: that understandability and rewrite-friendliness are related in a virtuous
 11 //: cycle. Doing one well makes it easier to do the other.
 12 //:
 13 //: Lower down, this file contains a legal, bare-bones C++ program. It doesn't
 14 //: do anything yet; subsequent files will contain :(...) directives to insert
 15 //: lines into it. For example:
 16 //:   :(after "more events")
 17 //: This directive means: insert the following lines after a line in the
 18 //: program containing the words "more events".
 19 //:
 20 //: A simple tool is included to 'tangle' all the files together in sequence
 21 //: according to their directives into a single source file containing all the
 22 //: code for the project, and then feed the source file to the compiler.
 23 //: (It'll drop these comments starting with a '//:' prefix that only make
 24 //: sense before tangling.)
 25 //:
 26 //: Directives free up the programmer to order code for others to read rather
 27 //: than as forced by the computer or compiler. Each individual feature can be
 28 //: organized in a self-contained 'layer' that adds code to many different data
 29 //: structures and functions all over the program. The right decomposition into
 30 //: layers will let each layer make sense in isolation.
 31 //:
 32 //:   "If I look at any small part of it, I can see what is going on -- I don't
 33 //:   need to refer to other parts to understand what something is doing.
 34 //:
 35 //:   If I look at any large part in overview, I can see what is going on -- I
 36 //:   don't need to know all the details to get it.
 37 //:
 38 //:   Every level of detail is as locally coherent and as well thought-out as
 39 //:   any other level."
 40 //:
 41 //:       -- Richard Gabriel, "The Quality Without A Name"
 42 //:          (http://dreamsongs.com/Files/PatternsOfSoftware.pdf, page 42)
 43 //:
 44 //: Directives are powerful; they permit inserting or modifying any point in
 45 //: the program. Using them tastefully requires mapping out specific lines as
 46 //: waypoints for future layers to hook into. Often such waypoints will be in
 47 //: comments, capitalized to hint that other layers rely on their presence.
 48 //:
 49 //: A single waypoint might have many different code fragments hooking into
 50 //: it from all over the codebase. Use 'before' directives to insert
 51 //: code at a location in order, top to bottom, and 'after' directives to
 52 //: insert code in reverse order. By convention waypoints intended for insertion
 53 //: before begin with 'End'. Notice below how the layers line up above the "End
 54 //: Foo" waypoint.
 55 //:
 56 //:   File 001          File 002                File 003
 57 //:   ============      ===================     ===================
 58 //:   // Foo
 59 //:   ------------
 60 //:              <----  :(before "End Foo")
 61 //:                     ....
 62 //:                     ...
 63 //:   ------------
 64 //:              <----------------------------  :(before "End Foo")
 65 //:                                             ....
 66 //:                                             ...
 67 //:   // End Foo
 68 //:   ============
 69 //:
 70 //: Here's part of a layer in color: http://i.imgur.com/0eONnyX.png. Directives
 71 //: are shaded dark.
 72 //:
 73 //: Layers do more than just shuffle code around. In a well-organized codebase
 74 //: it should be possible to stop loading after any file/layer, build and run
 75 //: the program, and pass all tests for loaded features. (Relevant is
 76 //: http://youtube.com/watch?v=c8N72t7aScY, a scene from "2001: A Space
 77 //: Odyssey".) Get into the habit of running the included script called
 78 //: 'test_layers' before you commit any changes.
 79 //:
 80 //: This 'subsetting guarantee' ensures that this directory contains a
 81 //: cleaned-up narrative of the evolution of this codebase. Organizing
 82 //: autobiographically allows newcomers to rapidly orient themselves, reading
 83 //: the first few files to understand a simple gestalt of a program's core
 84 //: purpose and features, and later gradually working their way through other
 85 //: features as the need arises.
 86 //:
 87 //: Programmers shouldn't need to understand everything about a program to
 88 //: hack on it. But they shouldn't be prevented from a thorough understanding
 89 //: of each aspect either. The goal of layers is to reward curiosity.
 90 
 91 // Includes
 92 // End Includes
 93 
 94 // Types
 95 // End Types
 96 
 97 // Function prototypes are auto-generated in the 'build' script; define your
 98 // functions in any order. Just be sure to declare each function header all on
 99 // one line, ending with the '{'. Our auto-generation scripts are too minimal
100 // and simple-minded to handle anything else.
101 #include "function_list"  // by convention, files ending with '_list' are auto-generated
102 
103 // Globals
104 //
105 // All statements in this section should always define a single variable on a
106 // single line. The 'build' script will simple-mindedly auto-generate extern
107 // declarations for them. Remember to define (not just declare) constants with
108 // extern linkage in this section, since C++ global constants have internal
109 // linkage by default.
110 //
111 // End Globals
112 
113 int main(int argc, char* argv[]) {
114   atexit(reset);
115   // we require a 32-bit little-endian system
116   assert(sizeof(int) == 4);
117   assert(sizeof(float) == 4);
118   assert_little_endian();
119 
120   // End One-time Setup
121 
122   // Commandline Parsing
123   // End Commandline Parsing
124 
125   // End Main
126 
127   return 0;
128 }
129 
130 // Unit Tests
131 // End Unit Tests
132 
133 //: our first directive; insert the following headers at the start of the program
134 :(before "End Includes")
135 #include <assert.h>
136 #include <stdlib.h>
137 
138 //: Without directives or with the :(code) directive, lines get added at the
139 //: end.
140 //:
141 //: Regardless of where functions are defined, we can call them anywhere we
142 //: like as long as we format the function header in a specific way: put it
143 //: all on a single line without indent, end the line with ') {' and no
144 //: trailing whitespace. As long as functions uniformly start this way, our
145 //: 'build' script contains a little command to automatically generate
146 //: declarations for them.
147 :(code)
148 void reset() {
149   // End Reset
150 }
151 
152 void assert_little_endian() {
153   const int x = 1;
154   const char* y = reinterpret_cast<const char*>(&x);
155   if (*y != 1) {
156     cerr << "SubX requires a little-endian processor. Do you have Intel (or AMD or Atom) inside?\n";
157     exit(1);
158   }
159 }
160 :(before "End Includes")
161 #include<iostream>
162 using std::cerr;