Code optimization

When not to attempt clever code optimization

• A macdef in ATS cannot involve types (but it can in ATS2); use macros only in cases where using functions would be inconvenient. Using macros probably does not make your code run more quickly, since gcc -O2 already inlines functions somewhat aggressively.

• Making use of the knowledge that separate val declarations within the same scope technically denote different vals on the stack should not preclude one from using a natural style. For instance:

    val x = 5
    val x = 7

here no extra space is allocated for the second 'x' due to constant propagation. It is in generally unlikely that such a coding style would incur any penalty.

Optimization tips

• Instead of freeing an instance of a linear type and immediately creating and returning a new one with the same value in a case expression, like this

  case+ x of
  | ~GRgenes (genes) => GRgenes (genes)
  

  do this

  case+ x of
  | GRgenes _ => (fold@ x; x)
  

  because @fold is compiled into a "noop".

• Remove anonymous closure definitions from function calls when possible, to avoid having them created each time the loop is called. For instance, a simple string comparison function can be created like so:

  val cmp_str = lam(x:string,y:string):int =<cloref> compare (x, y)