Introduction

Lua Fun is a high-performance functional programming library designed for LuaJIT tracing just-in-time compiler.

The library provides a set of more than 50 programming primitives typically found in languages like Standard ML, Haskell, Erlang, JavaScript, Python and even Lisp. High-order functions such as map(), filter(), reduce(), zip() will help you to write simple and efficient functional code.

Let’s see an example:

 -- Functional style
 require "fun" ()
 n = 100
 x = sum(map(function(x) return x^2 end, take(n, tabulate(math.sin))))
 -- calculate sum(sin(x)^2 for x in 0..n-1)
 print(x)
 50.011981355266

 -- Object-oriented style
 local fun = require "fun"
 n = 100
 x = fun.tabulate(math.sin):take(n):map(function(x) return x^2 end):sum()
 -- calculate sum(sin(x)^2 for x in 0..n-1)
 print(x)
 50.011981355266

Lua Fun takes full advantage of the innovative tracing JIT compiler to achieve transcendental performance on nested functional expressions. Functional compositions and high-order functions can be translated into efficient machine code. Can you believe it? Just try to run the example above with luajit -jdump and see what happens:

 -- skip some initialization code --
 ->LOOP:
 0bcaffd0  movsd [rsp+0x8], xmm7
 0bcaffd6  addsd xmm4, xmm5
 0bcaffda  ucomisd xmm6, xmm1
 0bcaffde  jnb 0x0bca0028        ->6
 0bcaffe4  addsd xmm6, xmm0
 0bcaffe8  addsd xmm7, xmm0
 0bcaffec  fld qword [rsp+0x8]
 0bcafff0  fsin
 0bcafff2  fstp qword [rsp]
 0bcafff5  movsd xmm5, [rsp]
 0bcafffa  mulsd xmm5, xmm5
 0bcafffe  jmp 0x0bcaffd0        ->LOOP
 ---- TRACE 1 stop -> loop

The functional chain above was translated by LuaJIT to (!) one machine loop containing just 10 CPU assembly instructions without CALL. Unbelievable!

Readable? Efficient? Can your Python/Ruby/V8 do better?