The Basic Language

Because we want to keep things simple, the only datatype in Kaleidoscope is a 64-bit floating point type (aka ‘double’ in C parlance). As such, all values are implicitly double precision and the language doesn’t require type declarations. This gives the language a very nice and simple syntax. For example, the following simple example computes Fibonacci numbers:

# Compute the x'th fibonacci number.
def fib(x)
  if x < 3 then
    1
  else
    fib(x-1)+fib(x-2);
# This expression will compute the 40th number.
fib(40);

We also allow Kaleidoscope to call into standard library functions (the LLVM JIT makes this completely trivial). This means that we can use the ‘extern’ keyword to define a function before we use it (this is also useful for mutually recursive functions). For example:

extern sin(arg);
extern cos(arg);
extern atan2(arg1 arg2);
atan2(sin(.4), cos(42));

A more interesting example is included in Chapter 6 where we write a little Kaleidoscope application that displays a Mandelbrot Set at various levels of magnification.

Let’s dive into the implementation of this language!