Update README.md

Author: ssloy

README.md

@@ -1,2 +1,49 @@
-# tinycompiler
-Writing a compiler in a week-end
+# tinycompiler - a 500-ish lines of code compiler in a weekend
+Have you ever wondered how a compiler works? If so, this project is for you.
+
+This weekend I'll write a compiler that translates a code written in a very simple programming language Wend (short for a week-end) into GNU assembly.
+This repository, however, will contain more than the final code. It will tell you a story about compilers.
+
+So behold, here is a program that uses virtually all concepts in Wend:
+```cpp
+fun main() {
+    // square root of a fixed-point number
+    // stored in a 32 bit integer variable, shift is the precision
+
+    fun sqrt(n:int, shift:int) : int {
+        var x:int;
+        var x_old:int;
+        var n_one:int;
+
+        if n > 65535 { // pay attention to potential overflows
+            return 2 * sqrt(n / 4, shift);
+        }
+        x = shift; // initial guess 1.0, can do better, but oh well
+        n_one = n * shift; // need to compensate for fixp division
+        while true {
+            x_old = x;
+            x = (x + n_one / x) / 2;
+            if abs(x - x_old) <= 1 {
+                return x;
+            }
+        }
+    }
+
+    fun abs(x:int) : int {
+        if x < 0 {
+            return -x;
+        } else {
+            return x;
+        }
+    }
+
+    // 25735 is approximately equal to pi * 8192;
+    // expected value of the output is sqrt(pi) * 8192 approx 14519
+
+    println sqrt(25735, 8192);
+}
+```
+
+There will no be dynamic memory allocation, no pointers, no garbage collection. There will be nested functions, function overloading and type checking.
+
+And as usual, there will be a program with a raytracer :)