Editing OCaml (section)

===MetaOCaml===
MetaOCaml<ref name = "Meta">{{cite web|url=http://okmij.org/ftp/ML/MetaOCaml.html|title=BER MetaOCaml|last=oleg-at-okmij.org|website=okmij.org}}</ref> is a [[multi-stage programming]] extension of OCaml enabling incremental compiling of new [[machine code]] during runtime. Under some circumstances, significant [[Speedup|speedups]] are possible using [[Multi-stage programming|multistage programming]], because more detailed information about the data to process is available at runtime than at the regular compile time, so the incremental compiler can optimize away many cases of condition checking, etc.

As an example: if at compile time it is known that some [[Exponentiation|power function]] {{OCaml|x -> x^n}} is needed often, but the value of {{OCaml|n}} is known only at [[Runtime system|runtime]], a two-stage power function can be used in MetaOCaml:

<syntaxhighlight lang="OCaml">
let rec power n x =
  if n = 0
  then .<1>.
  else
    if even n
    then sqr (power (n/2) x)
    else .<.~x *. .~(power (n - 1) x)>.
</syntaxhighlight>

As soon as {{OCaml|n}} is known at runtime, a specialized and very fast power function can be created:

<syntaxhighlight lang="OCaml">
.<fun x -> .~(power 5 .<x>.)>.
</syntaxhighlight>

The result is:

<syntaxhighlight lang="OCaml">
fun x_1 -> (x_1 *
    let y_3 = 
        let y_2 = (x_1 * 1)
        in (y_2 * y_2)
    in (y_3 * y_3))
</syntaxhighlight>

The new function is automatically compiled.